Apparatus and method for operating a real time large diopter range sequential wavefront sensor

ABSTRACT

A sequential wavefront sensor includes a light source, a beam deflecting element, a position sensing detector configured to output a plurality of output signals and a plurality of composite transimpedance amplifiers each coupled to receive an output signal. The output of each composite transimpedance amplifier is phase-locked to a light source drive signal and a beam deflecting element drive signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/745,738 filed Jan. 18, 2013, which is a continuation of U.S.application Ser. No. 13/198,442 filed Aug. 4, 2011 (now U.S. Pat. No.8,356,900 issued Jan. 22, 2013), which is a continuation-in-part of U.S.application Ser. No. 12/790,301 filed May 28, 2010, which is a divisionof U.S. application Ser. No. 11/761,890 filed Jun. 12, 2007, (now U.S.Pat. No. 7,815,310 issued Oct. 19, 2010), which is acontinuation-in-part of U.S. application Ser. No. 11/335,980 filed Jan.20, 2006 (now U.S. Pat. No. 7,445,335 issued Nov. 4, 2008); thisapplication is a continuation-in-part of U.S. application Ser. No.13/902,716 filed May 24, 2013, which is a continuation of U.S.application Ser. No. 13/354,763 filed Jan. 20, 2012, (now U.S. Pat. No.8,454,162 issued Jun. 4, 2013), which is a continuation of U.S.application Ser. No. 12/605,219 filed Oct. 23, 2009, (now U.S. Pat. No.8,100,530 issued Jan. 24, 2012), which is a continuation-in-part of U.S.application Ser. No. 11/761,890 filed Jun. 12, 2007, (now U.S. Pat. No.7,815,310 issued Oct. 19, 2010), which is a continuation-in-part of U.S.application Ser. No. 11/335,980 filed Jan. 20, 2006 (now U.S. Pat. No.7,445,335 issued Nov. 4, 2008); this application claims the benefit ofpriority to U.S. provisional application Ser. No. 61/723,531 filed Nov.7, 2012, each of which are incorporated by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

One or more embodiments of the present invention relate generally towavefront sensor(s) for use in vision correction procedures. Inparticular, the invention relates to the electronics and algorithms fordriving, controlling and processing the data of a real-time sequentialwavefront sensor and other subassemblies associated with the wavefrontsensor.

BACKGROUND OF THE INVENTION

Conventional wavefront sensors for human eye wavefront characterizationare generally designed to take a snap shot or several snap shots of apatient's eye wavefront with room lighting turned down or off. Thesewavefront sensors generally use a CCD or CMOS image sensor to capturethe wavefront data and need to use relatively complicated dataprocessing algorithms to figure out the wavefront aberrations. Due tothe fact that a CCD or CMOS image sensor generally has a limited numberof gray scales and cannot be operated at a frame rate well above the 1/fnoise range, these wavefront sensors therefore cannot take fulladvantage of lock-in detection scheme to provide higher signal to noiseratio. They cannot employ a simple algorithm to quickly derive thewavefront aberration. As a result, when these wavefront sensors areintegrated with an ophthalmic device such as a surgical microscope, theygenerally cannot provide accurate/repeatable real time wavefrontaberration measurement, especially with the microscope's illuminationlight turned on.

There is a need in the art for an apparatus and a method to not onlyrealize real time wavefront measurement and display, but also addressthe various issues including what has been mentioned above.

SUMMARY OF THE INVENTION

One or more embodiments satisfy one or more of the above-identifiedneeds in the art. In particular, one embodiment is an electronic controland driving circuit together with associated algorithm and software fordriving, controlling and processing the data of a real-time sequentialwavefront sensor to achieve various functions.

The circuit includes an opto-electronic position sensing detector/device(PSD) such as a quadrant photodiode/detector/cell/sensor or a lateraleffect position sensing detector, a transimpedance amplifier, an Analogto Digital (A/D) converter, a digital amplifier with programmable gaincontrol, a superluminescent diode (SLD or SLED) and its drive circuit, awavefront scanning/shifting device and its driver circuit, and afront-end data processing unit (e.g. processor, microcontroller, PGA,programmable device). In addition, a camera is used to provide livevideo images of the eye from which the wavefront is being measured.Furthermore, a back-end data processing unit is employed to convert thesequential wavefront data from the front-end processing unit to displayclinical ophthalmic information overlaid on or side-by-side with a liveimage of the patient's eye. The circuits (frontend and/or backend) canbe electronically connected to one or more various devices in one way oranother for coordinated operation of each device, including for example,an eye transverse position measurement device, an eye distancemeasurement device, an accommodation enabling eye fixation target, adata storage device, a laser based surgical ablation device, and adisplay device.

One embodiment of the present disclosure is to use a variable gainamplifier between the transimpedance amplifier and the A/D converter inthe above-mentioned circuit to realize a large signal strengthmeasurement over a larger signal strength dynamic range. The need forsuch a large signal strength measurement dynamic range arises from theneed to measure both weak and strong wavefront signals for various eyeor environmental conditions, such as a dense cataract eye versus anaphakic eye, or a long eye versus a short eye, or large distance fromthe eye, or bright external illumination

Another embodiment of the disclosure is to use a composite amplifierwith a high impedance feedback resistor as part of the transimpedanceamplifier to maximize signal-to-noise ratio, reduce electronic noise,and maintain amplifier stability without reducing gain-bandwidthproduct.

Still another embodiment of the disclosure is to combine a compositetransimpedance amplifier with a lock-in detection circuit to recoversmall signals which would otherwise be obscured by noise sources muchlarger than the signal of interest.

Still another embodiment is a wavefront sensor that includes a lightsource configured to output a light beam to illuminate a subject eye, alight source driver circuit, coupled to the light source, configured tooutput a light source drive signal at a first pulsing frequency, aposition sensitive detector having a plurality of detector elementsconfigured to output a plurality of detector output signals indicatingsignal strength of incident light on each detector element, a first beamdeflecting element configured to intercept a wavefront beam returnedfrom a subject eye when the subject eye is illuminated by the lightsource and configured to direct a portion of the wavefront from thesubject eye through an aperture toward the detector, where the portionof the wavefront directed through the aperture forms a spot on thedetector and with amplitude of deflection of a centroid of the spot froma reference point on the detector approximately indicated by aratiometric combination of the signal strengths and with the amplitudeof the deflection indicating the degree of tilt or convergence ordivergence of the portion of the wavefront from a plane wave, a beamdeflecting element driving circuit 720, coupled to the first beamdeflecting element, configured to output a beam deflecting element drivesignal to scan the portion of the wavefront at a wavefront scanningfrequency and a plurality of composite transimpedance amplifiers, eachhaving an input coupled to receive one of the plurality of detectoroutput signals and an output for providing an amplified detector outputsignal, with the output of each transimpedance amplifier phase-locked tothe light source drive signal and the beam deflecting element drivesignal.

These and other features and advantages of the present invention willbecome more readily apparent to those skilled in the art upon review ofthe following detailed description of the preferred embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example embodiment of the optical configuration of alarge diopter range real time sequential wavefront sensor integratedwith a surgical microscope;

FIG. 2 shows one example embodiment of electronics interfacing with theoptics of the wavefront sensor in FIG. 1 with those potentially activedevices connected to the electronic control circuit;

FIG. 3 shows what would happen to the wavefront sampling area on thecornea plane if the eye is transversely moved and there is nocorresponding change made to the wavefront sampling scheme.

FIG. 4 shows how, by DC offsetting the wavefront beam scanner, one cancompensate the transverse movement of the eye and hence continue to scanthe same properly centered annular ring even though the eye istransversely moved.

FIG. 5 illustrates what happens to the wavefront or refractive errorbeing measured if the eye is axially moved from the designed position.

FIG. 6 shows an overall block diagram of one example embodiment of anelectronics system that controls and drives the sequential wavefrontsensor and the associated devices shown in FIGS. 1 and 2;

FIG. 7 shows a block diagram of one example embodiment of the front-endelectronic processing system and the live imaging camera that resideswithin the sequential wavefront sensor module and the back-endelectronic processing system that resides in the host computer anddisplay module shown in FIG. 6;

FIG. 8 shows an example internal calibration target that can be movedinto the wavefront relay beam path to create one or more referencewavefront(s) for internal calibration and/or verification.

FIG. 9A shows an embodiment of an electronics block diagram thataccomplishes the task of automatic SLD index and digital gain control inorder to optimize the signal to noise ratio.

FIG. 9B shows a quadrant detector with firstly a light image spotlanding at the center and secondly landing slightly away from thecenter.

FIG. 9C shows a number of representative cases of planar wavefront,defocus and astigmatism, the associated image spot position on aquad-detector behind a subwavefront focusing lens, as well as thesequential movement of the corresponding centroid positions whendisplayed as a 2D data point pattern on a monitor.

FIG. 10 shows one example process flow block diagram in optimizing thesignal to noise ratio by changing the gain of the variable gainamplifier and the SLD output.

FIG. 11 shows one example embodiment of a composite transimpedanceamplifier with lock-in detection that can be used to amplify the signalfrom any one of the four quadrant photodiodes, as is used in theposition sensing detector circuit of FIG. 9;

FIG. 12 shows one example embodiment of the combination of aconventional transimpedance amplifier with a lock-in detection circuit;

FIG. 13A shows the case when the MEMS scan mirror is oriented so thatthe entire wavefront is shifted downward as the SLD pulse is fired. Inthis case the aperture samples a portion at the top of the circularwavefront section;

FIG. 13 B shows the case when the wavefront shifted leftward as the SLDpulse is fired so that the aperture samples a portion at the right ofthe of the circular wavefront section;

FIG. 13C shows that case when the wavefront is shifted upward as the SLDpulse is fired so that the aperture samples a portion at the bottom ofthe of the circular wavefront section;

FIG. 13D shows the case when the wavefront is shifted rightward as theSLD pulse is fired so that the aperture samples a portion at the left ofthe of the circular wavefront section;

FIG. 13E depicts the equivalence of the sequential scanning sequence offour pulses per cycle to sampling the wavefront section with fourdetectors arranged in a ring.

FIG. 13F shows the positions of 8 SLD pulse firing relative to the X andY axes of the MEMS scanner with 4 odd or even numbered pulses of the 8pulses aligned with the X and Y axes of the MEMS scanner and the other 4pulses arranged midway on the ring between the X and Y axes;

FIG. 14 shows an example in which the 4 SLD pulse firing positionsinitially aligned with the X and Y axes of the wavefront scanner asshown in FIG. 13F are shifted 15° away from the X and Y axes by slightlydelaying the SLD pulses;

FIG. 15 shows the collective effect of sampling a wavefront with offsetangle at 0° on the first frame, 15° on the second frame, and 30° on thethird;

FIG. 16 shows one example of a theoretically determined relationshipbetween the PSD ratiometric estimate and the actual centroiddisplacement or position along either the X or the Y axis;

FIG. 17 shows an example flow diagram that illustrates how calibrationcan be performed to obtain a modified relationship and to result in moreaccurate wavefront aberration measurement;

FIG. 18 shows a graphical representation of a sequential ellipse usingtrigonometry expressions, where U(t)=a·cos(t) and V(t)=b·sin(t), a>b>0,resulting in an ellipse that rotates counter-clockwise with the point(U(t₀), V(t₀)) in the first quadrant of the U-V Cartesian coordinate;

FIG. 19 shows a corresponding graphical representation of a similarsequential ellipse using trigonometry expression, where U(t)=−a·cos(t),V(t)=−b·sin(t), a>b>0, resulting in an ellipse that rotatescounter-clockwise with the point (U(t₀), V(t₀)) in the third quadrant ofthe U-V Cartesian coordinate;

FIG. 20 shows a corresponding graphical representation of a similarsequential ellipse using trigonometry expression, where U(t)=a·cos(t),V(t)=−b·sin(t), a>b>0, resulting in an ellipse that rotates clockwisewith the point (U(t₀), V(t₀)) in the fourth quadrant of the U-VCartesian coordinate;

FIG. 21 shows a corresponding graphical representation of a similarsequential ellipse using trigonometry expression, where U(t)=−a·cos(t),V(t)=b·sin(t), a>b>0, resulting in an ellipse that rotates clockwisewith the point (U(t₀), V(t₀)) in the second quadrant of the U-VCartesian coordinate;

FIG. 22 shows an example of the sequential centroid data points expectedfrom a divergent spherical wavefront and the resulting data pointposition and polarity;

FIG. 23 shows another example of the sequential centroid data pointsexpected from a convergent spherical wavefront and the resulting datapoint position and polarity;

FIG. 24 shows the Cartesian coordinate translation and rotation from theoriginal X-Y coordinate to the translated Xtr-Ytr coordinate and furtherrotated to the U-V coordinate of 8 sequentially sampled centroid datapoints that are fitted to a sequential ellipse.

FIG. 25 shows the result of coordinate rotation transformation and 8centroid data points on the U-V coordinate, with the left sidecorresponding to a divergent spherical wavefront having positive majorand minor axes, and with the right side corresponding to a convergentspherical wavefront, having negative major and minor axes;

FIG. 26 shows the process flow diagram of one example embodiment indecoding the sphere and cylinder diopter values and the cylinder axisangle;

FIG. 27 shows an example process flow diagram of an eye trackingalgorithm;

FIG. 28 shows an example process flow diagram illustrating the conceptof using the live eye image to determine the maximum wavefront samplingannular ring diameter and to obtain better diopter resolution forpseudo-phakic measurement;

FIG. 29 shows an example process flow diagram illustrating the conceptof using either the live eye image and/or the wavefront sensor signal todetect the presence of unintended object in the wavefront relay beampath or the moving away of the eye from a desired position range so thatthe SLD can be turned off and the erroneous “bright” or “dark” wavefrontdata can be abandoned;

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of theinvention. Examples of these embodiments are illustrated in theaccompanying drawings. While the invention will be described inconjunction with these embodiments, it will be understood that it is notintended to limit the invention to any embodiment. On the contrary, itis intended to cover alternatives, modifications, and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims. In the following description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe various embodiments. However, the present invention may be practicedwithout some or all of these specific details. In other instances, wellknown process operations have not been described in detail in order notto unnecessarily obscure nor apply limitations to the present invention.Further, each appearance of the phrase an “example embodiment” atvarious places in the specification does not necessarily refer to thesame example embodiment.

In a typical wavefront sensor used for the measurement of wavefrontaberration of a human eye, the wavefront from the eye pupil or corneaplane is generally relayed to a wavefront sensing or sampling planeusing the well known 4-F relay principle once or multiple times (see forexample, J. Liang, et al. (1994) “Objective measurement of the waveaberrations of the human eye with the use of a Hartmann-Shack wave-frontsensor,” J. Opt. Soc. Am. A 11, 1949-1957; J. J. Widiker, et al. (2006)“High-speed Shack-Hartmann wavefront sensor design with commercialoff-the-shelf optics,” Applied Optics, 45(2), 383-395; U.S. Pat. No.7,654,672). Such a single or multiple 4-F relay system will preserve thephase information of the incident wavefront while allowing it to berelayed without detrimental propagation effects. In addition, byconfiguring an afocal imaging system using two lenses of different focallengths to realize the 4-F relay, the relay can allow for themagnification or demagnification of the incident wavefront with anassociated demagnification or magnification of the divergence orconvergence of the incident wavefront (see for example, J. W. Goodman,Introduction to Fourier Optics, 2^(nd) ed. McGraw-Hill, 1996).

In recent years, it has been realized that there is a need for a realtime wavefront sensor to provide live feedback for various visioncorrection procedures such as LRI/AK refinement, Laser Enhancement, andcataract/refractive surgery. For these procedures, it has been realizedthat any interference to a normal surgical operation is undesirable,especially the turning off of the surgical microscope's illuminationlight and a waiting period for wavefront data capturing and processing.Surgeons want a real time feedback to be provided to them as the visioncorrection procedure is being normally performed. In addition, mostsurgeons also prefer that the real time wavefront measurement resultsbeing displayed continuously is synchronized and superimposed onto ordisplayed side-by-side next to a real time video display/movie of theeye, with the overlaid or side-by-side-displayed wavefront measurementresults shown in a qualitative or a quantitative or a combinedqualitative/quantitative manner. Another main issue is the movement ofthe eye relative to the wavefront sensor during a vision correctionsurgical procedure while the wavefront is being measured in real time.Previous wavefront sensors do not provide means to compensate for eyemovement; instead, they require the eye to be re-aligned to thewavefront sensor for meaningful wavefront measurement.

In a co-pending patent application (US20120026466) assigned to the sameassignee of this patent application, a large diopter range sequentialwavefront sensor especially suitable for addressing the issuesencountered during a vision correction procedure has been disclosed.Although details of many optical design/configuration possibilities havebeen disclosed in that co-pending patent application, the electronicscontrol and data processing details for operating such a large diopterrange sequential wavefront sensor have not been disclosed. Additionalmeasurement capabilities of different subassemblies have not beendiscussed in detail. In the present disclosure, various features of theelectronics control and driving aspects and the associated algorithm(s)for achieving various functions are disclosed.

In accordance with one or more embodiments of the present invention, alock-in detection electronics system associated with related algorithmsfor achieving high precision wavefront measurement is disclosed. Theelectronics system obtains its electronic signal from an opto-electronicposition sensing device/detector; it amplifies the analog signal with acomposite trans-impedance amplifier, converts the analog signal to adigital signal via an A/D converter, amplifies the digital signal via adigital amplifier, and processes the data via a data processing unit.The electronics system is connected to some or all of thoseelectronically active devices of the wavefront sensor module to achievedifferent functionalities. Examples of these active devices include alight source such as a superluminescent diode (SLD) for generating theobject wavefront to be measured, a SLD beam focusing and/or steeringmodule, a wavefront scanning/shifting device such as a MEMS scan mirror,an eye pupil transverse position and distance sensing/measurementdevice, an eye fixation target, various focus variable active lenses,one or more data processing and storage device(s), an end-user enabledinput device(s), and a display device.

FIG. 1 shows one example embodiment of the optical configuration of alarge diopter range real time sequential wavefront sensor integratedwith a surgical microscope and FIG. 2 shows the electronics connectionversion the wavefront sensor configuration of FIG. 1 with thosepotentially active devices connected to the electronics system.

In the embodiment of FIGS. 1 and 2, the first lens 104/204 of an 8-Fwavefront relay is arranged at the very first optical input port of thewavefront sensor module. The first lens 104/204 is shared by thesurgical microscope and the wavefront sensor module. The benefit ofarranging this first lens 104/204 of the 8-F wavefront relay as close aspossible to the patent eye is that the designed focal length of thisfirst lens can be the shortest per the requirement of an 8-F wavefrontrelay and accordingly the overall optical path length of the wavefrontsensor can be made the shortest. This combined with the folding of thewavefront relay beam path can make the wavefront sensor module compact.In addition, a larger diopter measurement range of the wavefront fromthe eye can be achieved when compared to a lens of the same diameter butarranged further downstream of the optical beam path. Furthermore, sincethere is always a need for the wavefront sensor to have an opticalwindow at this location, the lens therefore can serve the dual purposeof both the window and the first lens for the wavefront relay system aswell as for the microscope. However, it should be noted that the firstlens 104/204 can also be arranged after the dichroic or short pass beamsplitter 161/261.

The dichroic or short pass beam splitter 161/261 as shown in FIGS. 1 and2 is used to reflect/deflect with high efficiency the near infraredwavefront relay beam (covering at least the optical spectral range ofthe superluminescent diode or SLD 172/272) to the rest of the wavefrontsensor module while allowing most (for example ˜85%) of the visiblelight to pass through. The dichroic or short pass beam splitter 161/261can be designed to also allow a portion of the visible and/or nearinfrared light outside the SLD spectrum range to be reflected/deflectedso that a clear live image of the anterior of the patient eye can becaptured by an image sensor 162/262.

The compensating lens 102/202 above the dichroic or short pass beamsplitter 161/261 is used to fulfill several functions. Firstly, toensure that the surgical view to be formed and presented to the surgeonby the surgical microscope is not affected because of the use of thefirst lens 104/204 of the 8-F wavefront relay, this compensating lens102/202 can be designed to compensate the effect of the first lens104/204 to the microscopic view. Secondly, the compensating lens 102/202can serve as the upper optical window which can be needed for sealingthe wavefront sensor module. A third function of the compensating lens102/202 is to direct the illumination beam from the surgical microscopeaway from the optical axis so that when the illumination beam hits thelens 104/204, specular reflections from the lens 104/204 are notdirected back into the two stereoscopic viewing paths of the surgicalmicroscope to interfere with the surgeon's viewing of the surgicalscene. Finally, the compensating lens 102/202 can also be coated toallow only the visible spectrum of light to transmit through and toreflect and/or absorb the near infrared and ultraviolet spectrum oflight. In this manner, the near infrared spectral portion of light thatcorresponds to the SLD spectrum from the microscope illumination sourcewill not land on the patient eye to create any eye returned nearinfrared background light that can enter the wavefront sensor module toeither saturate the position sensing device/detector or to createbackground noise. Meanwhile, the coating can also reject or absorb anyultraviolet light from the illumination source of the microscope.However, it should be noted that if the first lens is arranged after thedichroic or short pass beam splitter 161/261, there will then be no needfor the compensation lens and a window with certain wavelength filteringfunction will be sufficient.

In FIGS. 1 and 2, the wavefront from the eye is relayed to a wavefrontsampling image plane 8-F downstream at which a wavefront samplingaperture 118/218 is disposed. The wavefront relay is accomplished usingtwo cascaded 4-F relay stages or an 8-F wavefront relay comprising, inaddition to the first lens 104/204, a second lens 116/216, a third lens140/240, and a fourth lens 142/242. The wavefront relay beam path isfolded by a polarization beam splitter (PBS) 174/274, a mirror 152/252and a MEMS beam scanning/shifting/deflecting mirror 112/212 to make thewavefront sensor module compact. Along the wavefront relay beam path, aband pass filter 176/276 can be arranged anywhere between the dichroicor short pass beam splitter 161/261 and the quadrant detector 122/222 tofilter out any light outside the SLD spectrum to reduce backgroundnoise. In addition, an aperture 177/277 can be arranged at the firstFourier transform plane between the PBS 174/274 and the mirror 152/252to serve the function of limiting the cone angle of the light rays fromthe eye and hence the diopter measurement range of the wavefront fromthe eye to a desired range as well as to prevent light from landingoutside the mirror surface area of the MEMS scanner 112/212 that isdisposed at the second Fourier transform plane.

The MEMS scan mirror 112/212 is disposed at the second Fourier transformplane of the 8-F wavefront relay to angularly scan the object beam sothat the relayed wavefront at the final wavefront image plane can betransversely shifted relative to the wavefront sampling aperture118/218. The wavefront sampling aperture 118/218 can be a fixed size oran active variable aperture. The sub-wavefront focusing lens 120/220behind the aperture 118/218 focuses the sequentially sampledsub-wavefront onto a position sensing device/detector (PSD) 122/222(such as a quadrant detector/sensor or a lateral effect position sensingdetector). It should be noted that the electronics system can at leastbe connected to the SLD 172/272, the wavefront shifting MEMS scan mirror112/212, and the PSD 122/222 to pulse the SLD, scan the MEMS mirror andcollect the signal from the PSD in synchronization such that lock-indetection can be realized.

At this point, it should be noted that although in FIGS. 1 and 2, thefirst lens of the wavefront relay is arranged at the input port locationof the wavefront sensor module or enclosure, this does not have to bethe case. The first lens 104/204 can be arranged after the dichroic orshort pass beam splitter 161/261 and a glass window can be arranged atthe input port location. Accordingly, the rest of the wavefront relaycan be redesigned and the optical function of the compensating lens orwindow 102/202 can be modified to ensure that good microscopic image ispresented to the surgeon.

In addition to the folded wavefront relay beam path, three more opticalbeam paths are shown in FIGS. 1 and 2, one for imaging the eye, one fordirecting a fixation target to the eye, and one for launching asuperluminescent diode (SLD) beam to the eye for the creation of thewavefront relay beam from the eye that carries the eye wavefrontinformation.

An imaging beam splitter 160/260 directs at least some of the imaginglight returned from the eye and reflected by the dichroic or short passbeam splitter 161/261 to an image sensor 162/262, such as a 2D pixelarray CCD/CMOS sensor, via a lens or set of lenses 168/268. The imagesensor 162/262 can be a black/white or color CMOS/CCD image sensorconnected to the electronics system. The image sensor 162/262 provides acoplanar video or static image of a subject eye and can be focused toimage either the anterior or the posterior of the eye. Further, afixation/imaging beam splitter 166/266 directs the image of a fixationtarget 164/264, formed by a lens or set of lenses 170/270 together withthe first lens 104/204, along a reverse path to the patient eye. Thelens 168/268 in front of the image sensor 162/262 can be designed towork with the first lens 104/204 to provide a desired opticalmagnification for the live image of the anterior or posterior of thepatient eye on a display (not shown in FIGS. 1 and 2) and be used toadjust focus either manually or automatically if needed to ensure thatthe image sensor plane is conjugate with, for example, the eye pupilplane so that a clear eye pupil image can be obtained. In the automaticfocusing case, the lens 168/268 needs to be connected to the electronicssystem.

The lens 170/270 in front of the fixation target 164/264 can be designedto provide the patient eye with a comfortable fixation target of theright size and brightness. It can also be used to adjust focus to ensurethat the fixation target is conjugate with the retina of the eye, or tofixate the eye at different distances, orientations, or even to fog theeye. In doing so, the lens 170/270 needs to be made active and beconnected to the electronics system. The fixation light source 164/264can be driven by the electronics system to flash or blink at a ratedesired to differentiate it from, for example, the illumination light ofa surgical microscope. The color of the fixation light source 164/264can also change. The fixation target can be a micro-display with itsdisplayed patterns or spot(s) variable to the desire of asurgeon/clinician. In addition, a micro-display based fixation targetcan also be used to guide the patient to gaze at different directions sothat a 2D array of eye aberration map can be measured and generated,which can be used to assess the visual acuity of a patient's peripheralvision.

The fixation target 164/264 can be a red or green or yellow (or anycolor) light emitting diode (LED) with its output optical powerdynamically controllable by the electronics system based on differentbackground lighting conditions. For example, when a relatively strongillumination beam from a surgical microscope is turned on, thebrightness of the fixation light source 164/264 can be increased toenable the patient to easily find the fixation target and fixate on it.A variable diaphragm or aperture (not shown in FIG. 1 or FIG. 2) canalso be arranged in front of the lens 168/268 before the image sensorand connected to the electronics system to control the depth of field ofthe live image of the anterior or posterior of the eye. By dynamicallychanging the aperture size, the degree of blurriness of the eye imagewhen the eye is axially moved away from the designed distance can becontrolled, and the relationship between the blurriness of the eye imageand the eye axial location as a function of the diaphragm or aperturesize can be used as a signal to determine the axial distance of the eye.As an alternative, the eye distance can also be measured through wellknown means such as triangulation based on cornea scattered/reflectedimage spot locations of one or more near infrared illumination sources.Low coherence interferometry based eye distance measurement as will bedisclosed below can also be employed.

A ring or multiple rings of LEDs (or arrays) (135/235) can be arrangedencircling around the input port of the wavefront enclosure to servemultiple functions. One function is to simply provide flood illuminationlight within a wavelength spectral range so that eye returned lightwithin this spectrum can reach the image sensor (162/262). In this way,if there is no illumination from the surgical microscope or if theillumination light from the surgical microscope has been filtered toonly allow visible light to reach the eye, the contrast of the eye imageas captured by the image sensor (162/262) can be kept to within adesired range. As one example, the image sensor is a monochromeUI-1542LE-M which is an extremely compact board-level camera having 1.3Megapixel resolution (1280×1024 pixels). An NIR band pass filter can bedisposed along the imaging path so that only the flood illuminationlight will reach the image sensor to maintain a relatively constantcontrast of the live eye image.

A second function of the LEDs (135/235) is to create specular reflectionimage spots returned from the optical interfaces of the cornea and/orthe eye lens (natural or artificial) so that Purkinje images of the LEDs(135/235) can be captured by the image sensor (162/262). Through imageprocessing of these Purkinje images, the transverse position of thepatient eye can be determined. In addition, the top and/or bottomsurface profile or the topograph of the cornea and/or the eye lens(natural or artificial) can be figured out in the same way as a cornealtopographer and/or a keratometer/keratoscope does. This informationobtained can be used to determine change(s) in the cornea shape or evensome other eye biometric/anatomic parameters. The measured change canthen be used to set a targeted or expected refraction during or rightafter the refractive surgery so that when the incision or wound made inthe cornea of the eye is completely healed, the final refraction of theeye will be as desired.

A third function of the LEDs (135/235) can be that some can beselectively turned on and projected onto the white of the eye to createlight spots that can be captured by the image sensor (162/262) torealize eye distance measurement using the principle of opticaltriangulation. The change in the centroid position of the imaged lightspots can be processed to figure out the eye distance.

In addition to providing a live eye pupil/iris or cornea image and toimage the flood illumination effects, the image sensor signal can alsobe used for other purposes. For example, the live image can be used todetect the size, distance from the first lens (104/204), and transverseposition of the eye pupil. When it is found that the size of the pupilis small, the wavefront sampling area can be correspondingly reduced. Inother words, the pupil size information can be used in a closed loopmanner for the automatic and/or dynamic adjustment and/or the scaling ofwavefront sensing area per the pupil size.

One embodiment of this disclosure is the correction of wavefrontmeasurement error as a result of eye position change within certainposition range. The correction can be applied to both eye transverseposition change as well as eye axial position change. In one embodiment,when it is found that the eye or pupil is not centered well enough, i.e.aligned well enough with respect to the optical axis of the wavefrontsensor, the amount of transverse movement of the eye or the pupilrelative to the wavefront sensor module is determined and used to eithercorrect for the measured wavefront error that would be introduced bysuch an eye or pupil position transverse movement, or to adjust thedrive signal of the wavefront sampling scanner so that the same area onthe cornea is always sampled.

The transverse position of the eye or the pupil can be determined usingthe live eye image or other means. For example, the limbus can provide areference to where eye is; the border between the pupil and the iris canalso provide the reference to where the eye is. In addition, specularlyreflected flood illumination light from the cornea anterior surfacecaptured by the live eye camera as bright light spots or detected byadditional position sensing detectors can also be used to provide theinformation on the transverse position of the eye. Furthermore,specularly reflected SLD light from the cornea anterior surface can alsobe captured by the live eye camera as bright light spots or detected byadditional position sensing detectors to determine the transverseposition of the eye. The SLD beam can also be scanned in two dimensionsto search for the strongest cornea apex specular reflection and todetermine the eye transverse position.

FIG. 3 shows what would happen to the wavefront sampling area on thecornea plane if the eye is transversely moved and there is nocorresponding change made to the wavefront sampling scheme. Assume thatthe SLD beam is coaxial with and fixed in space relative to thewavefront sensor optical axis and the wavefront sensor is samplingaround a radially or rotationally symmetric annular ring with respect tothe optical axis of the wavefront sensor on the corneal plane. When theeye is well aligned, the SLD beam 302 would enter the eye through theapex of the cornea and the center of the pupil, land on the retina nearthe fovea. The returned wavefront would therefore be sampled within aradially or rotationally symmetric annular ring centered with respect tothe apex of the cornea or the center of the eye pupil as shown by theannular ring 304 of the cross-sectional corneal plane view on the right.Now imagine if the eye is transversely moved downward with respect tothe SLD beam and the wavefront sensor. The SLD beam 312 would now enterthe eye off-centered, but still land on the retina near the fovea,although the exact location may be slightly different depending on theaberration of the eye. Since the wavefront sampling area is fixedrelative to the SLD beam, on the corneal plane the sampled annular ringwould, therefore, be shifted upward relative to the apex of the corneaor the center of the eye pupil as shown by the annular ring 314 of thecross-sectional corneal plane view on the right. This non-radially ornon-rotationally symmetric wavefront sample would therefore causewavefront measurement errors. In one embodiment of the presentdisclosure, with the information on the transverse position of the eyeor the pupil, the wavefront measurement errors are corrected usingsoftware and data processing.

In one embodiment of the present disclosure, with the information on thetransverse position of the eye or the pupil, the SLD beam can be scannedto follow or track the eye or the pupil so that the SLD beam will alwaysenter the cornea from the same cornea location as designed (such as aposition slightly off the apex of the cornea), to, for example, preventspecularly reflected SLD beam returned by the cornea from entering thewavefront sensor's PSD. The live eye image can also be used to determinethe presence of the eye, and to turn on or off the SLD/wavefrontdetection system accordingly. To ensure that the SLD beam always entersthe eye at a desired cornea location and is not blocked partially orfully by the iris as a result of eye transverse movement (within acertain eye movement range), a scan mirror 180/280 for scanning the SLDbeam as shown in FIGS. 1 and 2 can be positioned at the back focal planeof the first wavefront relay lens 104/204. In this case, an angular scanof the scan mirror 180/280 will cause a transverse scan of the SLD beamwith respect to the cornea plane. The image sensor captured live imageof the eye or other eye transverse position detection means can be usedto figure out the transverse position of the eye center and to provide afeedback signal to drive the scan mirror 180/280 to enable the SLD beamto follow the eye movement or track the eye.

In another embodiment of the present disclosure, the wavefront beamscanner 112/212 is driven with a proper DC offset to follow the eyetransverse movement or to track the eye so that wavefront sampling isalways done over the same area of the eye pupil. For example, thesampling can be done over an annular ring that is radially orrotationally symmetric with respect to the center of the eye pupil. Inorder to see how this is possible, let us recall that the wavefront beamscanner is located at the second Fourier transfer plane of the 8-Fwavefront relay configuration. When the eye is transversely moved, atthe 4-F wavefront image plane, the image of the wavefront will also betransversely moved with a proportional optical magnification orde-magnification depending on the focal length ratio of the first andsecond lenses. If the wavefront beam scanner does not do any scanningand there is no DC offset, when this transversely moved wavefront at theintermediate wavefront image plane is further relayed to the finalwavefront sampling image plane, it will also be transversely displacedwith respect to the sampling aperture. As a result, when the wavefrontbeam scanner does an angular rotational scan. The effective scannedannular ring area on the corneal plane will be de-centered as shown bythe lower portion of FIG. 3.

FIG. 4 shows how, by DC offsetting the wavefront beam scanner, one cancompensate the transverse movement of the eye and hence continue to scanthe same properly centered annular ring even though the eye istransversely moved. As can be seen in FIG. 4, when there is a transversemovement of the eye, the SLD beam 448 would enter the eye off-centeredand the wavefront at the cornea plane as an object to be relayed by the8-F relay is also off-axis. The intermediate wavefront image 402 istherefore transversely displaced and if there is no DC offset of thewavefront beam scanner, without the scanning of the wavefront beam atthe second Fourier transform image plane, the intermediate wavefrontimage would be relayed to the final wavefront sampling plane as atransversely displaced wavefront image 432 as well. In this case, if thewavefront beam scanner scans in the form of circular angular rotationrelative to a zero DC offset angle, the sampled wavefront will then be anon-radially or non-rotationally symmetric annular ring with respect tothe center of the eye as shown by the annular ring 444. However, if thewavefront beam scanner 462 as shown on the right side of FIG. 4 has acertain DC offset properly determined based on the transversedisplacement of the eye, then the final wavefront image 482, whenrelayed to the final wavefront sampling image plane, can be transverselydisplaced to be re-centered with respect to the wavefront samplingaperture 458. In this case, the SLD beam 498 would still enter the eyeoff-centered, the wavefront at the cornea plane as an object to berelayed by the 8-F relay is off-axis when passing through the first,second and third lenses, but after the wavefront scanner, the relay iscorrected by the wavefront scanner and is now on-axis. Accordingly,further angular rotational scanning of the wavefront beam scannerrelative to this DC offset angle would result in the sampling of aradially or rotationally symmetric annular ring 494 with respect to thecenter of the eye.

One embodiment of the present disclosure is therefore to control the DCoffset of the wavefront scanner in response to the transverse movementof the eye that can be determined by the live eye camera or other means.Owing to the fact that along the wavefront relay path, the wavefrontimaging is done not on-axis but off-axis along some of the imaging path,there can therefore be other optical aberrations introduced, including,for example, coma and prismatic tilt. These additional aberrationsintroduced as a result of off-axis wavefront relaying can be taken careof through calibration and be treated as if there is inherent aberrationof an optical imaging or relay system and hence can be subtracted usingcalibration and data processing.

In another embodiment of the present disclosure, when it is found thatthe eye is not axially positioned at the designed distance from theobject plane of the wavefront sensor, the amount of axial displacementof the eye relative to the designed axial position is determined and theinformation is used to correct for the measured wavefront error thatwould be introduced by such an eye axial movement. FIG. 5 illustrateswhat happens to the wavefront or refractive error being measured if theeye is axially moved from the designed position.

On the left column of FIG. 5, three emmetropic eyes are shown with thetop one 504 moved further away from the wavefront sensor, with themiddle one 506 at the designed axial location of the wavefront sensorand the bottom one 508 moved towards the wavefront sensor. As can beseen, since the wavefront emerging from this emmetropic eye is planar,at the designed object plane 502 from which the wavefront will berelayed to the final wavefront sampling plane, the wavefronts 514, 516and 518 are all planar for the three cases. Therefore, when the eye isemmetropic, if the eye is slightly displaced axially from the designedposition, the wavefront measurement result will not be affected.

However, if the eye is myopic as shown by the middle column of FIG. 5where the crystalline lens (525, 527, 529) of the eye is shown asthicker and the eye (524, 526, 528) is also drawn as longer, thewavefront emerging from the eye will converge to a point (535, 537, 539)and the dioptric value of the wavefront at the corneal plane isdetermined by the distance from the corneal plane of the eye to theconvergent point. In this case, if the eye is moved slightly furtheraway from the wavefront sensor, as shown by the top example of themiddle column, the wavefront at the object plane 522 of the wavefrontsensor is not the same as the wavefront at the corneal plane of the eye.In fact, the convergent radius of curvature of the wavefront at theobject plane of the wavefront sensor is smaller than that at the cornealplane. Therefore, when this wavefront 534 at the object plane of thewavefront sensor is measured by the wavefront sensor, the measuredresult will be different from the wavefront 536 at the corneal plane asthe radius of curvature of the wavefront 534 is smaller than the radiusof curvature of the wavefront 536. If, on the other hand, the eye ismoved closer towards the wavefront sensor as shown by the bottom exampleof the middle column, the wavefront 538 at the object plane 522 of thewavefront sensor is again not the same as the wavefront 536 at thecorneal plane of the eye. In fact the radius of curvature of thewavefront 538 at the object plane of the wavefront sensor is now largerthan the wavefront 536 at the corneal plane. As a result, the measuredwavefront result at the wavefront object plane will again be differentfrom that at the corneal plane of the eye.

When the eye is hyperopic as shown by the right column of FIG. 5 wherethe crystalline lens of the eye is removed and the eye (544, 546, 548)is also drawn as shorter than normal to simulate a short aphakic eye,the wavefront emerging from the eye will be divergent and by extendingthe divergent light rays backward, one can find a virtual focus point(555, 557, 559) from which the light rays originate. The hyperopicdioptric value of the wavefront at the corneal plane is determined bythe distance from the corneal plane of the eye to the virtual focuspoint. In this case, if the eye is moved further away from the wavefrontsensor, as shown by the top example of the right column, the wavefront554 at the object plane 542 of the wavefront sensor is again not thesame as the wavefront 556 at the corneal plane of the eye. In fact, thedivergent radius of curvature of the wavefront 554 at the object planeof the wavefront sensor is now larger than the divergent radius ofcurvature of the wavefront 556 at the corneal plane. Therefore, whenthis wavefront 554 at the object plane of the wavefront sensor ismeasured by the wavefront sensor, the measured result will again bedifferent from the wavefront 556 at the corneal plane. If, on the otherhand, the eye is moved closer towards the wavefront sensor as shown bythe bottom example of the right column, the wavefront 558 at the objectplane 542 of the wavefront sensor will still be different from thewavefront 556 at the corneal plane of the eye. In fact, the radius ofcurvature of the divergent wavefront 558 at the object plane of thewavefront sensor will now be smaller than the wavefront 556 at thecorneal plane. As a result, the measured wavefront result at thewavefront object plane will again be different from that at the cornealplane of the eye.

In one embodiment of the present disclosure a real time means to detectthe axial position of the eye under test is incorporated and in realtime the information on the amount of axial movement of the eye relativeto the wavefront sensor module's object plane is used to correct for themeasured wavefront error that would be introduced by such an eye axialmovement. As will be discussed later, the eye axial position measurementmeans include optical triangulation and optical low coherenceinterferometry as is well known to those skilled in the art. Acalibration can be done to determine the relationship between the axialposition of the eye, and the true wavefront aberration of the eye versusthe wavefront aberration at the object plane of the wavefront sensor asmeasured by the wavefront sensor. A look up table can then beestablished and used in real time to correct for the wavefrontmeasurement errors. In the case of a cataract surgery, the surgicalmicroscope, when fully zoomed-out, can generally present to a surgeon arelatively sharp-focused view of the patient eye within an axial rangeof the order of about ±2.5 mm. So when the surgeon focuses a patient eyeunder a surgical microscope, the variation in the patient eye's axialposition should be within a range of about ±2.5 mm. Therefore, thecalibration can be done over such a range and the look-up table can beestablished also over such a range.

In one example embodiment of the present disclosure, when it is foundthat the eye is being irrigated with water/solution, or there areoptical bubbles, or the eye lid is in the optical path, or facial skin,or a surgeon's hand, or a surgical tool or instrument, is in the imagesensor's view field and is blocking the wavefront relay beam pathpartially or fully, the wavefront data can be abandoned/filtered toexclude the “dark” or “bright” data and at the same time, the SLD172/272 can be turned off. In another example embodiment of the presentdisclosure, the wavefront sensor is used to figure out if the eye is dryand a reminder in the form of video or audio signal can be sent to thesurgeon or clinician to remind him/her when to irrigate the eye.Moreover, the signal from the image sensor 162/262 can also be used toidentify if the patient eye is in a phakic, or aphakic or pseudo-phakicstate and accordingly, the SLD pulses can be turned on during only theneeded period. These approaches can reduce the patient's overallexposure time to the SLD beam and thus possibly allow higher peak poweror longer on-duration SLD pulses to be used to increase the wavefrontmeasurement signal to noise ratio. Additionally, an algorithm can beapplied to the resultant eye image to determine optimal distance to theeye through the effective blurriness of the resultant image, and/or intandem with triangulation fiducials.

In FIGS. 1 and 2, a large size polarization beam splitter (PBS) 174/274is used for launching the SLD beam to the patient eye. The reason forusing a large window size is to ensure that the wavefront relay beamfrom an eye over a desired large diopter measurement range is notpartially, but fully, intercepted by the PBS 174/274. In the exampleembodiment, the beam from the SLD 172/272 is preferably p-polarized sothat the beam substantially transmits through the PBS 174/274 and islaunched to the eye for creating the eye wavefront. The SLD beam can bepre-shaped or manipulated so that when the beam enters the eye at thecornea plane, it can be either collimated or focused or partiallydefocused (either divergently or convergently) at the cornea plane. Whenthe SLD beam lands on the retina as either a relatively small light spotor a somewhat extended light spot, it will be scattered over arelatively large angular range, and the returned beam thus generatedwill have both the original polarization and an orthogonal polarization.As is well known to those skilled in the art, for ophthalmic wavefrontsensor applications, only the orthogonal polarization component of thewavefront relay beam is used for eye wavefront measurement. This isbecause in the original polarization direction, there exist relativelystrongly reflected SLD light waves from the cornea and the eye's lenswhich can introduce errors to the wavefront measurement. So anotherfunction of the large PBS 174/274 is to only allow the orthogonallypolarized wavefront relay beam to be reflected by the PBS 174/274 and todirect the returned light waves polarized in the original direction tobe transmitted through the PBS 174/274 and absorbed or used for otherpurpose such as to monitor if there is specular reflection of the SLDbeam by the cornea or eye lens back into the wavefront sensor module.

In FIGS. 1 and 2, a band pass filter 176/276 is arranged in thewavefront relay beam path to reject any visible light and/or ambientbackground light, and to only allow the desired relatively narrowspectrum of the wavefront relay beam light that the SLD generates toenter the rest of the wavefront sensor module.

In addition to the fact that the SLD beam can be scanned to follow eyetransverse movement, the SLD beam can also be scanned to land over asmall scanned area on the retina with the control from the electronicssystem which includes the front end electronic processor and the hostcomputer. In one example embodiment, to ensure that the SLD beam alwaysenters the eye at a desired cornea location and is not blocked partiallyor fully by the iris as a result of eye movement (within a certain eyemovement range), a scan mirror 180/280 for scanning the SLD beam asshown in FIGS. 1 and 2 can be positioned at the back focal plane of thefirst wavefront relay lens 104/204. In this case, an angular scan of thescan mirror 180/280 will cause a transverse scan of the SLD beam withrespect to the cornea plane but still allow the SLD beam to land on thesame retina location if the eye is emmetropic. The image sensor capturedlive image of the eye pupil can be used to figure out the transverseposition of the eye pupil center and to provide a feedback signal todrive the scan mirror 180/280 and to enable the SLD beam to follow theeye movement or track the eye.

In one example embodiment, to enable the SLD beam to land and also scanaround a small area on the retina, another scan mirror 182/282 as shownin FIGS. 1 and 2 can be positioned conjugate to the cornea plane at theback focal plane of a SLD beam shape manipulation lens 184/284. Anotherlens 186/286 can be used to focus or collimate or shape the SLD beamfrom the output port of, for example, a single mode optical fiber (suchas a polarization maintaining (PM) single mode fiber) 188/288, onto thescan mirror 182/282. The scanning of the SLD beam over a small area onthe retina can provide several benefits; one is to reduce speckleeffects resulting from having the SLD beam always landing on the sameretina spot area, especially if the spot size is very small; anotherbenefit is to divert the optical energy over a slightly larger retinalarea so that a higher peak power or longer on-duration pulsed SLD beamcan be launched to the eye to increase the signal to noise ratio foroptical wavefront measurement; and still another benefit is to enablethe wavefront measurement to be averaged over a slightly larger retinalarea so that wavefront measurement errors resulting from retinaltopographical non-uniformity can be averaged out or detected and/orquantified. As an alternative, by controlling the focusing andde-focusing of the SLD beam using the lens 186/286 (or 184/284), the SLDbeam spot size on the retina can also be controlled to achieve similargoals.

It should be noted that the scanning of the SLD beam relative to thecornea and the retina can be performed independently, simultaneously,and also synchronized. In other words, the two SLD beam scanners 180/280and 182/282 can be activated independently of each other but at the sametime. In addition, it should be noted that a laser beam as an eyesurgery light beam (not shown In FIGS. 1 and 2) can be combined with theSLD beam and delivered to the eye through the same optical fiber orthrough another free space light beam combiner to be delivered to thesame scanner(s) for the SLD beam or other scanners so that the eyesurgery laser beam can be scanned for performing refractive surgery ofthe eye such as limbal relaxing incision (LRI), or other cornealsculpting. The SLD and the eye surgery laser can have differentwavelengths and be combined using optical fiber based wavelengthdivision multiplexing couplers or free space dichroic beam combiners.

An internal calibration target 199/299 can be moved into the wavefrontrelay beam path when a calibration/verification is to be made. The SLDbeam can be directed to be coaxial with the wavefront relay optical beampath axis when the internal calibration target is moved in place. Thecalibration target can be made from a material that will scatter lightin a way similar to an eye retina with maybe some desired attenuation sothat a reference wavefront can be generated and measured by thesequential wavefront sensor for calibration/verification purpose. Thegenerated reference wavefront can be either a nearly planer wavefront ora typical aphakic wavefront, or a divergent or convergent wavefront ofany other degree of divergence/convergence.

Although for eye wavefront measurement, only the beam returned from theretina with an orthogonal polarization is used, this does not mean thatthose returned light waves from the cornea, the eye's lens, and theretina with the original polarization are useless. On the contrary,these returned light waves with the original polarization can providevery useful information. FIG. 1 and 2 show that the eye returned lightwaves with the original polarization can be used for the measurement ofeye distance from the wavefront sensor module, the location of the eye'slens (either natural or implanted) in the eye (i.e. effective lensposition), the anterior chamber depth, the eye length and other eyeanterior and/or posterior biometric or anatomic parameters. In FIGS. 1and 2, the returned light waves that pass through the PBS 174/274 iscollected with a low coherence fiber optic interferometer as istypically employed for optical low coherence interferometry (OLCI) oroptical coherence tomography (OCT) measurements. The SLD output fiber188/288 can be single mode (SM) (and polarization maintaining (PM) ifdesired) and can be connected to a normal single mode (SM) fiber (or apolarization maintaining (PM) single mode optical fiber) coupler so thatone portion of the SLD light is sent to the wavefront sensor and anotherportion of the SLD light is sent to a reference arm 192/292. The opticalpath length of the reference arm can be roughly matched to thatcorresponding to optical path length of the light waves returned fromthe eye. The light wave returned from different parts of the eye can bemade to recombine with the reference light wave returned through thereference fiber arm 192/292 at the fiber coupler 190/290 to result inoptical low coherence interference. This interference signal can bedetected by the detector 194/294 as shown in FIGS. 1 and 2. Note thatalthough in FIGS. 1 and 2, the same fiber coupler 190/290 is used forboth splitting and recombining the light waves in a Michelson type ofoptical interferometer configuration, other well known fiber opticinterferometer configurations can all be used as well, one example is aMach-Zehnder type configuration using two fiber couplers with a fibercirculator in the sample arm to efficiently direct the sample armreturned light wave to the recombining fiber coupler.

Various OLCI/OCT configurations and detection schemes, includingspectral domain, swept source, time domain, and balanced detection, canbe employed. In order to keep the wavefront sensor module (to beattached, for example, to a surgical microscope or a slit lampbio-microscope) compact, the detection module 194/294, the reference arm192/292 (including the reference mirror plus the fiber loop), and eventhe SLD 172/272 and the fiber coupler 190/290, can be located outsidethe wavefront sensor enclosure. The reason for doing this is that thedetection module 194/294 and/or the reference arm 192/292 and/or the SLDsource 172/272 can be bulky depending on the scheme being used for theOLCI/OCT operation. The electronics for operating the OLCI/OCTsub-assembly can be located either inside the wavefront sensor enclosureor outside the wavefront sensor enclosure. For example, when a balanceddetection scheme is employed as discussed in U.S. Pat. No. 7,815,310, afiber optic circulator (not shown) may need to be incorporated in theSLD fiber arm. When time domain detection is employed, the reference arm192/292 may need to include an optical path length scanner or a rapidscanning optical delay line (not shown), which needs to be controlled bythe electronics. When spectral domain detection scheme is employed, thedetection module may need to include an optical spectrometer and a linescan camera (not shown), which needs to be controlled by theelectronics. When swept source detection scheme is employed, the lightsource may need to include a wavelength scanner (not shown), which needsto be controlled by the electronics.

In one example embodiment, in order to ensure that a relatively strongOLCI/OCT signal can be collected, the scan mirror(s) 180/280 (and/or182/282) can be controlled by the electronics system to specifically letrelatively strong specular reflections from, for example, the cornea,the eye's lens (natural or artificial) and the retina, to return to theoptic fiber interferometer so that axial distance of the opticalinterfaces of these eye components with respect to the wavefront sensormodule or relative to each other can be measured. This operation can besequentially separated from the eye wavefront measurement as in thelatter case, specular reflection should perhaps be avoided.Alternatively, two different wavelength bands can be used and spectralseparation can be employed. On the other hand, the OLCI/OCT signalstrength can be used as an indication on whether specular reflection isbeing collected by the wavefront sensor module and if yes, the wavefrontsensor data can be abandoned.

In another example embodiment, the SLD beam can be scanned across theanterior segment of the eye or across a certain volume of the retina andbiometric or anatomic structure measurement of the various parts of theeye can be made. One particularly useful measurement is the corneasurface and thickness profile.

In one example embodiment, the beam scanner 112/212 used forshifting/scanning the wavefront and those (180/280, 182/282) used forscanning the SLD beam can also have a dynamic DC offset to bringadditional benefits to the present disclosure. For example, the scanner112/212 used for shifting and/or scanning the wavefront can be utilizedto provide compensation to potential misalignment of the opticalelements as a result of environmental changes such as temperature toensure that wavefront sampling is still rotationally symmetric withrespect to the center of the eye pupil. Meanwhile, the reference pointon the position sensing device/detector (PSD) can also be adjusted ifneeded per the compensated image spot locations through a calibration.If there is any angular DC offset of the sampled image spots relative tothe PSD reference point, this can be taken care of through calibrationand data processing. We mentioned that the scanner 180/280 used forscanning the SLD beam can be employed to follow eye transverse movementwithin a certain range through a feedback signal from the image sensor162/262. With the eye moved relative to the wavefront sensor module,even though the SLD beam can be made to enter the eye through the samecornea location at the same angle as it would when the eye is centeredwell relative to the wavefront sensor module, the returned wavefrontbeam from the eye will be transversely displaced relative to the opticalaxis of the wavefront sensor module. As a result, the relayed wavefrontat the wavefront sampling image plane will also be transverselydisplaced. In this case, the DC offset of the scanner 112/212 used forshifting the wavefront can be employed to compensate for thisdisplacement and still make the scanned wavefront beam rotationallysymmetric with respect to the wavefront sampling aperture 118/218. Inthis case, there can be coma or prismatic tilt or other additionalaberration introduced, these can be taken care of through calibrationand data processing. In doing so, any wavefront measurement errorinduced by the change in the eye position/location can be compensated orcorrected.

With the combination of information provided by the image sensor, thewavefront sensor, the specular reflection detector and/or the lowcoherence interferometer, it is possible to combine some or all theinformation to realize an auto selection of the correct calibrationcurve and/or the correct data processing algorithm. Meanwhile, a dataintegrity indicator, or a confidence indicator, or a cataract opacitydegree indicator, or an indicator for the presence of optical bubblescan be shown to the surgeon or clinician through audio or video or othermeans, or connected to other instruments in providing feedback. Thecombined information can also be used for intraocular pressure (IOP)detection, measurement and/or calibration. For example, a patient heartbeat generated or an external acoustic wave generated intraocularpressure change in the anterior chamber of the eye can be detected bythe wavefront sensor and/or the low coherence interferometer insynchronization with an oximeter that monitors the patient heart beatsignal. A pressure gauge equipped syringe can be used to injectviscoelastic gel into the eye to inflate the eye and also measure theintraocular pressure. The combined information can also be used todetect and/or confirm the centering and/or tilt of an implantedintraocular lens (IOL) such as a multi-focal intraocular lens. Thecombined information can also be used for the detection of the eyestatus, including phakia, aphakia and pseudophakia. The wavefront sensorsignal can be combined with the OLCI/OCT signal to measure and indicatethe degree of optical scattering and/or opacity of the eye lens or theoptical media of the ocular system. The wavefront sensor signal can alsobe combined with the OLCI/OCT signal to measure tear film distributionover the cornea of the patient eye.

One requirement for real time ophthalmic wavefront sensor is a largediopter measurement dynamic range that can be encountered during acataract surgery, such as when the natural eye lens is removed and theeye is aphakic. Although the optical wavefront relay configuration hasbeen designed to cover a large diopter measurement dynamic range, thesequential nature has eliminated the cross talk issue, and the lock-indetection technique can filtered out DC and low frequency 1/f noises,the dynamic range can still be limited by the position sensingdevice/detector (PSD). In one embodiment, the optics is optimallydesigned so that over the desired the diopter coverage range, theimage/light spot size on the PSD is always within a certain range suchthat its centroid can be sensed by the PSD. In another embodiment, adynamic wavefront/defocus offsetting device 178/278 as shown in FIGS. 1and 2 is disposed at the intermediate wavefront image plane, i.e. the4-F plane which is conjugate to both the cornea plane and the wavefrontsampling plane. The dynamic wavefront/defocus offsetting device 178/278can be a drop-in lens, a focus variable lens, a liquid crystal basedtransmissive wavefront manipulator, or a deformable mirror basedwavefront manipulator. In the case that the PSD becomes the limitingfactor for measuring a large diopter value (positive or negative), theelectronics system can activate the wavefront/defocus offsetting device178/278 to offset or partially/fully compensate some or all of thewavefront aberrations. For example, in the aphakic state, the wavefrontfrom the patient's eye is relatively divergent, a positive lens can bedropped into the wavefront relay beam path at the 4-F wavefront imageplane to offset the spherical defocus component of the wavefront andtherefore to bring the image/light spot landing on the PSD to within therange such that the PSD can sense/measure the centroid of sequentiallysampled sub-wavefronts.

In other cases like high myopia, high hyperopia, relatively largeastigmatism or spherical aberrations, the wavefront/defocus offsettingdevice 178/278 can be scanned and deliberate offsetting can be appliedto one or more particular aberration component(s) in a dynamic manner.In this way, some lower order aberrations can be offset and informationon other particular higher order wavefront aberrations can behighlighted to reveal those clinically important feature(s) of theremaining wavefront aberrations that need to be further corrected. Indoing so, the vision correction practitioner or surgeon can fine tunethe vision correction procedure and minimize the remaining wavefrontaberration(s) in real time.

FIG. 6 shows an overall block diagram of one example embodiment of theelectronics system 600 that controls and drives the sequential wavefrontsensor and other associated active devices as shown in FIGS. 1 and 2. Inthis embodiment, a power module 605 converts AC power to DC power forthe entire electronics system 600. The wavefront data and theimages/movies of the eye can be captured and/or recorded insynchronization in a stream manner. The host computer & display module610 provides back-end processing that includes synchronizing a live eyeimage with the wavefront measurement result, and a visible display tothe user with the wavefront information overlaid on or displayedside-by-side with the live image of the patient eye. The host computer &display module 610 can also convert the wavefront data into computergraphics which are synchronized and blended with the digitalimages/movies of the eye to form a composite movie and display thecomposite movie on the display that is synchronized to real-timeactivity performed during a vision correction procedure.

The host computer & display module 610 also provides power andcommunicates with the sequential wavefront sensor module 615 throughserial or parallel data link(s) 620. The optics as shown in FIGS. 1 and2 reside together with some front-end electronics in the sequentialwavefront sensor module 615. In one embodiment of the presentdisclosure, the host computer & display module 610 and sequentialwavefront sensor module 615 communicate through a USB connection 620.However any convenient serial, parallel, or wireless data communicationprotocol will work. The host computer & display module 610 can alsoinclude an optional connection 625 such as Ethernet to allow downloadingof wavefront, video, and other data processed or raw onto an externalnetwork (not shown in FIG. 6) for other purposes such as later dataanalysis or playback.

It should be noted that the display should not be limited to a singledisplay shown as combined with the host computer. The display can be abuilt-in heads up display, a semi-transparent micro display in theocular path of a surgical microscope, a back-projection display that canproject information to overlay on the live microscopic view as seen by asurgeon/clinician, or a number of monitors mutually linked among oneanother. In addition to overlaying the wavefront measurement data ontothe image of the patient eye, the wavefront measurement result (as wellas the other measurement results such as those from the image sensor andthe low coherence interferometer) can also be displayed adjacently ondifferent display windows of the same screen or separately on differentdisplays/monitors.

Compared with prior art wavefront sensor electronics systems, thepresent electronics system is different in that the host computer &display module 610 is configured to provide back-end processing thatincludes synchronizing a live eye image with the sequential wavefrontmeasurement data and at the same time, displays the synchronizedinformation by overlaying the wavefront information on the live eyeimage or displaying the wavefront information side-by-side next to thelive eye image. In addition, the front-end electronics (as will bediscussed shortly) inside the sequential wavefront sensor module 615operates the sequential real time ophthalmic wavefront sensor in lock-inmode, and is configured to send the front-end processed wavefront datato be synchronized with the live eye image data to the host computer anddisplay module 610.

FIG. 7 shows a block diagram of one example embodiment of the front-endelectronic processing system 700 that resides within the wavefrontsensor module 615 shown in FIG. 6. In this embodiment, a live imagingcamera module 705 (such as a CCD or CMOS image sensor/camera) provides alive image of the patient eye, the data of which is sent to the hostcomputer and display module 610 as shown in FIG. 6 so that the wavefrontdata can be overlaid on the live image of the patient's eye. A front-endprocessing system 710 is electronically coupled to the SLD drive andcontrol circuit 715 (which, in addition to pulsing the SLD, may alsoperform SLD beam focusing and SLD beam steering as has been discussedbefore with regard to FIGS. 1 and 2), to the wavefront scanner drivingcircuit 720, and to the position sensing detector circuit 725. Comparedto prior art wavefront sensor electronics systems, the presentlydisclosed front-end electronic processing system has a number offeatures that when combined in one way or another make it different andalso advantageous for real time ophthalmic wavefront measurement anddisplay, especially during eye refractive cataract surgery. The lightsource used for creating the wavefront from the eye is operated in pulseand/or burst mode. The pulse repetition rate or frequency is higher(typically in or above the kHz range) than the typical frame rate of astandard two dimensional CCD/CMOS image sensor (which is typically about25 to 30 Hz (generally referred to as frames per second)). Furthermore,the position sensing detector is two dimensional with high enoughtemporal frequency response so that it can be operated in lock-indetection mode in synchronization with the pulsed light source at afrequency above the 1/f noise frequency range. The front-end processingsystem 710 is at least electronically coupled to the SLD drive andcontrol circuit 715, the wavefront scanner driving circuit 720, and theposition sensing detector circuit 725. The front-end electronics isconfigured to phase-lock the operation of the light source, thewavefront scanner, and the position sensing detector.

In addition, the front-end processing system 710 can also beelectronically coupled to an internal fixation and LEDs driving circuit730, and an internal calibration target positioning circuit 735. Inaddition to driving the internal fixation as discussed before withreference to FIGS. 1 and 2, the LEDs driving circuit 730 can includemultiple LED drivers and be used to drive other LEDs, includingindicator LEDs, flood illumination LEDs for the eye live imaging camera,as well as LEDs for triangulation based eye distance ranging. Theinternal calibration target positioning circuit 735 can be used toactivate the generation of a reference wavefront to be measured by thesequential wavefront sensor for calibration/verification purpose.

The front-end and back-end electronic processing systems include one ormore digital processors and non-transitory computer readable memory forstoring executable program code and data. The various control anddriving circuits 715-735 may be implemented as hard-wired circuitry,digital processing systems or combinations thereof as is know in theart.

FIG. 8 shows an example internal calibration and/or verification target802/832/852 that can be moved into the wavefront relay beam path tocreate one or more reference wavefront(s) for internal calibrationand/or verification. In one embodiment, the internal calibration and/orverification target comprises a lens (such as an aspheric lens) 804 anda diffusely reflective or scattering material such as a piece ofspectralon 806. The spectralon 806 can be positioned a short distance infront of or beyond the back focal plane of the aspheric lens 804. Theaspheric lens 804 can be anti-reflection coated to substantially reduceany specular reflection from the lens itself.

When the internal calibration and/or verification target 802 is movedinto the wavefront relay beam path, it would be stopped by, for example,a magnetic stopper (not shown), such that the aspheric lens 804 iscentered and coaxial with the wavefront relay optical axis. The SLD beamwould then be intercepted by the aspheric lens with minimum specularreflection and the SLD beam would be focused, at least to some extent,by the aspheric lens to land on the spectralon 806 as a light spot.Since the spectralon is designed to be highly diffusely reflectiveand/or scattering, the returned light from the spectralon will be in theform of a divergent cone 812 and after travelling backward through theaspheric lens, it will become a slightly divergent or convergent beam oflight 814.

The position of the internal calibration target as shown in the FIGS. 1and 2 is somewhere between the first lens 104/204 and the polarizationbeam splitter 174/274, therefore a somewhat slightly divergent orconvergent beam there propagating backward would be equivalent to a beamcoming from a point source in front of or behind the object plane of thefirst lens 104/204. In other words, the internal calibration and/orverification target created reference wavefront is equivalent to aconvergent or divergent wavefront coming from an eye under test.

In one embodiment, the actual axial position of the spectralon relativeto the aspheric lens can be designed such that the reference wavefrontcan be made to resemble that from an aphakic eye. In another embodiment,the actual axial position of the spectralon can be designed such thatthe reference wavefront thus created can be made to resemble that froman emmetropic or a myopic eye.

It should be noted that although we used an aspheric lens here, aspherical lens and any other type of lens, including cylindrical plusspherical lens or even a tilted spherical lens can be used to create areference wavefront with certain intended wavefront aberrations forcalibration and/or verification. In one embodiment, the position of thespectralon relative to the aspheric lens can also be continuously variedso that the internally created wavefront can have continuously variablediopter values to enable a complete calibration of the wavefront sensorover the designed diopter measurement range.

In another embodiment, the internal calibration target can simply be abare piece of spectralon 836. In this case, the requirement on the stopposition of the piece of spectralon 836 can be lessened as any part of aflat spectralon surface, when moved into the wavefront relay beam path,can intercept the SLD beam to generate substantially the same referencewavefront assuming that the topographic property of the spectralonsurface is substantially the same. In this case, the emitted beam fromthe bare piece of spectralon will be a divergent beam 838.

In still another embodiment, the internal calibration and/orverification target comprises both a bare piece of spectralon 866 andalso a structure with an aspheric lens 854 and a piece of spectralon856, where the spectralon (866 and 856) can be a single piece. Themechanism to move the internal calibration and/or verification target852 into the wavefront relay beam path can have two stops, anintermediate stop that does not need to be very repeatable and a finalmagnetic stopping position that is high repeatable. The intermediatestopping position can be used to enable the bare piece of spectralon tointercept the SLD beam and the highly repeatable stopping position canbe used to position the aspheric lens plus spectralon structure so thatthe aspheric lens is centered well and coaxial with the wavefront relaybeam optical axis. In this way, one can obtain two reference wavefronts(864 and 868) and hence use the internal calibration target to check ifthe system transfer function behaves as designed or if there is any needto compensate for any misalignment of the wavefront relay opticalsystem.

Due to the difference in the amount of light returned from a real eyeversus that returned from a piece of spectralon, an optical attenuationmeans, such as a neutral density filter and/or a polarizer, can beincluded in the internal calibration and/or verification target and bedisposed either in front of or behind the aspheric lens to attenuate thelight so that it is about the same as that from a real eye.Alternatively, the thickness of the spectralon can be properly selectedto only enable a desired amount of light to be diffusely back scatteredand/or reflected and the transmitted light can be absorbed by a lightabsorbing material (not shown in FIG. 8).

One embodiment of the present invention is to interface the front-endprocessing system 710 with the position sensing detector circuit 725 andthe SLD driver and control circuit 715. As the position sensor detectoris likely a parallel multiple channel one in order for it to have highenough temporal frequency response, it can be a quadrantdetector/sensor, a lateral effect position sensing detector, a parallelsmall 2D array of photodiodes, or others. In the case of a quadrantdetector/sensor or a lateral effect position sensing detector, there aretypically 4 parallel signal channels. The front-end processing systemcomputes ratio-metric X and Y values based on signal amplitudes fromeach of the 4 channels (A, B, C and D) as will be discussed later. Inaddition to the standard practice, the front-end processing system can(upon user discretion) automatically adjust SLD output and the gain ofthe variable gain amplifier either independently for each of thechannels or together for all the channels so that the final amplifiedoutputs of the A, B, C and D values for all sequentially sampledsub-wavefront image spots landing on the position sensing detector areoptimized for optimal signal-to-noise ratio. This is needed because theoptical signal returned from a patient eye can vary depending on therefractive state (myopic, emmetropic and hyperopic), the surgical state(phakic, aphakic and pseudo-phakic), and degree of cataract of the eye.

FIGS. 9A and 9B show an embodiment of an electronics block diagram thataccomplishes the task of automatic SLD index and digital gain controlthrough a servo mechanism in order to optimize the signal to noiseratio, and FIG. 10 shows an example embodiment in the form of a processflow block diagram.

Referring to FIG. 9A, the microprocessor 901 is coupled to a memory unit905 that has code and data stored in it. The microprocessor 901 is alsocoupled to the SLD 911 via a SLD driver and control circuit with digitalto analog conversion 915, the MEMS scanner 921 via a MEMS scannerdriving circuit with digital to analog conversion 925, and the PSD 931via a composite transimpedance amplifier 933, an analog to digitalconverter 935 and a variable gain digital amplifier 937.

It should be noted that the PSD in this example is a quadrant detectorwith four channels that lead to four final amplified digital outputs A,B, C, and D, so correspondingly, there are four composite transimpedanceamplifiers, four analog to digital converters and four variable gaindigital amplifiers, although in FIG. 9A only one of each is drawn.

To illustrate the points, we will briefly repeat with reference to FIG.9B what has been discussed in US7445335. Assume that a sequentialwavefront sensor is used for wavefront sampling and a PSD quad-detector931 with four photosensitive areas of A, B, C, and D is used to indicatethe local tilt in terms of the centroid position of the sampledsub-wavefront image spot position as shown in FIG. 9B. If thesub-wavefront is incident at a normal angle with respect to thesub-wavefront focusing lens in front of the quad-detector 931, the imagespot 934 on the quad-detector 931 will be at the center and the fourphotosensitive areas will receive the same amount of light, with eacharea producing a signal of the same strength. On the other hand, if thesub-wavefront departs from normal incidence with a tilting angle (say,pointing toward the right-upper direction), the image spot on thequad-detector will then be formed away from the center (moved towardsthe right-upper quadrant as shown by the image spot 938).

The departure (x, y) of the centroid from the center (x=0, y=0) can beapproximated to a first order using the following equation:

$\begin{matrix}{{x = \frac{\left( {B + C} \right) - \left( {A + D} \right)}{A + B + C + D}}{y = \frac{\left( {A + B} \right) - \left( {C + D} \right)}{A + B + C + D}}} & (1)\end{matrix}$

where A, B, C and D stand for the signal strength of each correspondingphotosensitive area of the quad-detector and the denominator (A+B+C+D)is used to normalize the measurement so that the effect of opticalsource intensity fluctuation can be cancelled. It should be noted thatEquation (1) is not perfectly accurate in calculating the local tilt interms of the centroid position, but it is a good approximation. Inpractice, there may be a need to further correct the image spot positionerrors that can be induced by the equation using some mathematics and abuilt-in algorithm.

Referring to FIG. 10, at the beginning step 1002, the front endmicroprocessor 901 preferably sets the SLD initially to an output levelas much as allowed per eye safety document requirement. The gain of thevariable gain digital amplifier 937 at this moment can be initially setat a value determined at the last session or at an intermediate value aswould normally be selected.

The next step (1004) is to check the variable gain digital amplifierfinal outputs A, B, C and D. If the amplified final outputs of A, B, Cand D values are found to be within the desired signal strength range,which can be the same for each channel, the process flow moves to thestep 1006 at which the gain of variable gain digital amplifier is keptat the set value. If any or all of the final outputs are below thedesired signal strength range, the gain can be increased as shown bystep 1008 and the final outputs are then checked as shown by step 1010.If the final outputs are within the desired range, the gain can be setas shown by step 1012 at a value slightly higher than the current valueto overcome fluctuation induced signal variations that can cause thefinal outputs to go outside the desired range again. If the finaloutputs are still below the desired signal strength range and the gainhas not reached its maximum as shown to be checked by step 1014, theprocess of increasing the gain per step 1008 and checking the finaloutputs per step 1010 can be repeated until the final outputs fallwithin the range and the gain is set as shown by step 1012. One possibleexceptional scenario is that the final outputs are still below thedesired range when the gain is already increased to its maximum as shownby step 1014. In this case, the gain will be set at its maximum as shownby step 1016 and data can still be processed, but a statement can bepresented to the end user to inform him/her that the wavefront signal istoo weak so the data might be invalid as shown by step 1018.

On the other hand, if any of the final outputs A, B, C and D are abovethe desired signal strength range, the gain of the variable gain digitalamplifier can be decreased as shown by step 1020 and the final outputsare checked as shown by step 1022. If all of the final outputs arewithin the desired range, the gain can be set as shown by step 1024 at avalue slightly lower than the current value to overcome fluctuationinduced signal variations that can cause the final outputs to go outsidethe desired range again. If any of the final outputs is still above thedesired signal strength range and the gain has not reached its minimumas checked at step 1026, the process of decreasing the gain per step1020 and checking the final outputs per step 1022 can be repeated untilthe final outputs all fall within the range and the gain is set as shownby step 1024.

However, there is a possibility that the gain has reached its minimumwhen checked at step 1026 and one or more of the final outputs A, 13, Cand D is(are) still above the desired signal strength range. In thiscase, the gain is kept at its minimum as shown at step 1028 and the SLDoutput can be decreased as shown by step 1030. The final outputs A, B, Cand D are checked at step 1032 after the SLD output is decreased and ifit is found that the final A, B, C and D outputs are within the desiredrange, the SLD output is then set as shown by step 1034 at a levelslightly lower than the current level to overcome fluctuation inducedsignal variations that can cause the final outputs to go outside thedesired range again. If one or more of the final outputs A, B, C and Dis(are) still above the desired range and the SLD output has not reachedzero per the checking step of 1036, the process of decreasing the SLDoutput as shown by step 1030 and checking the final A, B, C and Doutputs as shown by step 1032 can be repeated until they reach thedesired range and the SLD output is set as shown by step 1034. The onlyexception is that the SLD output has reached zero and one or more of thefinal A, B, C and D outputs is(are) still above the desired range. Thismeans that even if there is no SLD output; there is still a strongwavefront signal. This can only happen when there is either electronicor optical interference or cross talk. We can keep the SLD output atzero as shown by step 1038 and send the end user a message that there isstrong interference signal so data is invalid as shown by step 1040.

In addition to the above, as an alternative, the end user can alsomanually control the SLD output and the gain of the variable gaindigital amplifier until he/she feels that the real wavefront measurementresult is satisfactory.

It should be noted that the example embodiment given in FIGS. 9A and 9Band FIG. 10 is only one of many possible ways to achieve the same goalof improving the signal to noise ratio, so it should be considered asillustrating the concept. For example, at the beginning step, there isno absolute need to set the SLD output to the level as much as allowedper eye safety document requirement. The SLD output can be initially setat any arbitrary level and then adjusted together with amplifier gainuntil the final outputs A, B, C and D fall within the desired range. Theadvantage of setting the SLD output initially to a relatively high levelis that in the optics or photonics domain, the optical signal to noiseratio before any opto-electronic conversion can be maximized. However,this does not mean that other choices would not work. In fact, the SLDoutput can even be initially set at zero and gradually increasedtogether with the adjustment of the amplifier gain until the final A, B,C and D outputs fall within the desired range. In this case, there willbe a corresponding change to the sequence and details of the processflow. These variations should be considered as within the scope andspirit of the present disclosure.

Another embodiment of the present disclosure is to use a compositetransimpedance amplifier to amplify the position signal of a sequentialophthalmic wavefront sensor. FIG. 11 shows one example embodiment of acomposite transimpedance amplifier that can be used to amplify thesignal from any one quadrant (for example, D1) of the four quadrantphotodiodes of a quadrant detector. The circuit is used in the positionsensing detector circuit as shown in FIG. 9A. In this compositetransimpedance amplifier, the current-to-voltage conversion ratio isdetermined by the value of the feedback resistor R1 (which, for example,can be 22 MegOhms) and is matched by resistor R2 to balance the inputsof the op-amp U1A. The shunt capacitors C1 and C2 could be eitherparasitic capacitance of resistors R1 and R2 or small capacitors addedto the feedback loop. The transimpedance amplifier's stability andhigh-frequency noise reduction comes from the low-pass filter formed byresistor R3, capacitor C3 and op-amp U2A inside the feedback loop 1150.In this circuit, +Vref is some positive reference voltage between groundand +Vcc. Since the output signal (Output A) is proportional to R1, butnoise is proportional to the square root of RE the signal-to-noise ratiotherefore increases proportionally to the square root of R1 (since it isdominated by the Johnson noise of R1).

Note that prior art high-bandwidth wavefront sensors generally only usestandard transimpedance amplifier(s) rather than compositetransimpedance amplifier(s) (see, for example, S. Abado, et. al.“Two-dimensional High-Bandwidth Shack-Hartmann Wavefront Sensor: DesignGuidelines and Evaluation Testing”, Optical Engineering, 49(6), 064403,June 2010.). In addition, prior art wavefront sensors are not purelysequential but parallel in one way or another. Furthermore, they do notface the same weak but synchronized and pulsed optical signal challengeas the present sequential ophthalmic wavefront sensor faces. Featuresthat, when combined in one way or another, are uniquely associated withthe presently disclosed composite transimpedance amplifier in terms ofits application to the amplification of the optical signal in asequential ophthalmic wavefront sensor include the following: (1) Inorder to improve the current to voltage conversion precision, theselected feedback resistor value of R1 that is substantially matched byresistor R2 is very high; (2) In order to reduce the noise contributionfrom the large resistance value of R1 and R2 while maintaining adequatesignal bandwidth, the two shunt capacitors C 1 and C2 have very lowcapacitance values; (3) The low-pass filter formed by R3, C3 and U2Ainside the feedback loop substantially improves the stability and alsosubstantially reduces the high-frequency noise of the transimpedanceamplifier; (4) To achieve lock-in detection, the positive referencevoltage+Vref is a properly scaled DC signal phase-locked to the drivesignal of the SLD and the MEMS scanner, and it is between ground and+Vcc. Furthermore, to achieve optimal signal to noise ratio, a quadrantsensor with minimal terminal capacitance is preferably selected; and toavoid any shunt conductance between any two of the four quadrants, goodchannel isolation between the quadrants is preferred.

In addition to the above circuit, the optical signal converted to ananalog current signal by the position sensing detector can also be ACcoupled to and amplified by a conventional transimpedance amplifier, andthen combined with a standard lock-in detection circuit to recover smallsignals which would otherwise be obscured by noises that can be muchlarger than the signal of interest. FIG. 12 shows one example embodimentof such a combination. The output signal from the transimpedanceamplifier 1295 is mixed at a mixer 1296 with (i.e. multiplied by) theoutput of a phase-locked loop 1297 which is locked to the referencesignal that drives and pulses the SLD. The output of the mixer 1296 ispassed through a low-pass filter 1298 to remove the sum frequencycomponent of the mixed signal and the time constant of the low-passfilter is selected to reduce the equivalent noise bandwidth. Thelow-pass filtered signal can be further amplified by another amplifier1299 for analog to digital (A/D) conversion further down the signalpath.

An alternative to the above lock-in detection circuit is to activate theA/D conversion just before the SLD is illuminated to record a “dark”level, and activate the A/D conversion just after the SLD is illuminatedto record a “light” level. The difference can then be computed to removethe effects of interference. Yet another embodiment is to activate theA/D conversion just after the SLD is illuminated or record a “light”level while ignoring the “dark” levels if interference effects areminimal.

In addition to the optical signal detection circuit, the next criticalelectronically controlled component is the wavefront scanner/shifter. Inone embodiment, the wavefront scanner/shifter is an electromagnetic MEMS(Micro-Electro-Mechanical System) analog steering mirror driven by fourD/A converters controlled by the microprocessor. In one example, twochannels of D/A converters output sinusoids 90 degrees apart in phase,and the other two channels output X and Y DC-offset voltages to steerthe center of the wavefront sampling annular ring. The amplitude of thesine and cosine electronic waveforms determines the diameter of thewavefront sampling annular ring, which can be varied to accommodatevarious eye pupil diameters as well as to deliberately sample around oneor more annular ring(s) of the wavefront with a desired diameter withinthe eye pupil area. The aspect ratio of the X and Y amplitude can alsobe controlled to ensure that a circular scanning is done when the mirrorreflects the wavefront beam sideways.

FIGS. 13A to 13F illustrate how synchronizing the MEMS scanner and SLDpulses create the same result as if the wavefront were sampled bymultiple detectors arrayed in a ring.

In FIG. 13A the MEMS 1312 is oriented so that the entire wavefront isshifted downward when the SLD pulse is fired. In this case the aperture1332 samples a portion at the top of the circular wavefront section.

In FIG. 13 B the wavefront shifted leftward so that the aperture samplesa portion at the right of the of the circular wavefront section, in FIG.13C the wavefront is shifted upward so that the aperture samples aportion at the bottom of the of the circular wavefront section and inFIG. 13D the wavefront is shifted rightward so that the aperture samplesa portion at the left of the of the circular wavefront section.

FIG. 13E depicts the equivalence of the sequential scanning sequence offour pulses per cycle to sampling the wavefront section with fourdetectors arranged in a ring.

In another example, the SLD can be synchronized with the MEMS scannerand 8 SLD pulses can be fired to allow 8 sub-wavefronts to be sampledper each MEMS scanning rotation and hence each wavefront samplingannular ring rotation. The SLD pulse firing can be timed such that 4 oddor even numbered pulses of the 8 pulses are aligned with the X and Yaxes of the MEMS scanner and the other 4 pulses are arranged midway onthe ring between the X and Y axes. FIG. 13F shows the resulting patternof the MEMS scanning rotation and the relative SLD firing positions. Itshould be noted that the number of SLD pulses does not need to berestricted to 8 and can be any number, the SLD pulses do not need to beequally spaced in time, and they do not have to be aligned with the Xand Y axes of the MEMS scanner.

As an alternative, for example, by changing the relative timing and/orthe number of pulses of SLD firing with respect to the driving signal ofthe MEMS scanner, we can shift the wavefront sampling positions alongthe wavefront sampling annular ring to select the portion of thewavefront to be sampled and also to achieve higher spatial resolution interms of sampling the wavefront. FIG. 14 shows an example in which the 8wavefront sampling positions are shifted 15° away from those shown inFIG. 13F by slightly delaying the SLD pulses.

As another alternative, if we sample the wavefront with offset angle at0° on the first frame, 15° on the second frame, and 30° on the thirdframe and repeat this pattern, we can sample the wavefront withincreased spatial resolution when data from multiple frames arecollectively processed. FIG. 15 shows such a pattern. Note that thisframe-by-frame gradual increase in the initial firing time of the SLDcan be implemented with any desired but practical timing precision toachieve any desired spatial resolution along any annular wavefrontsampling ring. In addition, by combining the change in the amplitude ofthe MEMS scanner's sinusoidal and co-sinusoidal drive signals, we canalso sample different annular rings with different diameters. In thisway, sequential sampling of the whole wavefront can be achieved with anydesired spatial resolution in both the radial and also angular dimensionof a polar coordinate system. It should be noted that this is only oneexample of many possible sequential wavefront scanning/sampling schemes.For example, a similar approach can be applied to the case of rasterscanning.

As described above, with reference to FIG. 9B, in terms of interpretingthe centroid position of different sequentially sampled sub-wavefrontimage spots landing on the position sensing device/detector (PSD),standard well known ratiometric equations can be used. It is preferredthat a quadrant detector or lateral-effect position sensing detector isused as the PSD and its X-Y axis is aligned in orientation to that ofthe MEMS scanner so that they have the same X and Y axis, although thisis not absolutely required. In the case of, for example, a quadrantdetector, the ratiometric X and Y values of a sequentially sampledsub-wavefront image spot can be expressed based on the signal strengthfrom each of the four quadrants, A, B, C, and D as:X=(A+B−C−D)/(A+B+C+D)Y=(A+D−B−C)/(A+B+C+D)

In general, these ratiometric values of X and Y do not directly givehighly accurate transverse displacement or position of the centroids,because the response of, for example, a quadrant detector is also afunction of gap distance, the image spot size which is dependent on anumber of factors, including the local average tilt and the localdivergence/convergence of the sampled sub-wavefront, as well as thesub-wavefront sampling aperture shape and size. One embodiment of thepresent invention is to modify the relationship or equation so that thesampled sub-wavefront tilt can be more precisely determined.

In one embodiment, the relationship between the ratiometric measurementresult and the actual centroid displacement is theoretically and/orexperimentally determined and the ratiometric expression is modified tomore accurately reflect the centroid position. FIG. 16 shows one exampleof a theoretically determined relationship between the ratiometricestimate and the actual centroid displacement or position along eitherthe X or the Y axis.

Because of this non-linearity, an approximate inverse of the effect canbe applied to the original equation to result in a modified relationshipbetween the ratiometric (X, Y) and the actual centroid position (X′,Y′). Below is just one example of such an inverse relationship.X′=PrimeA*X/(1−X ²/PrimeB)Y′=PrimeB*Y/(1−Y ²/PrimeB)where PrimeA and PrimeB are constants.

It should be noted that the relationship or equation shown above isillustrative, it is not intended to be a limitation to the possibleapproaches that can be used to achieve the same goal. In fact, the abovemodification is for the centroid position of a sampled sub-wavefront ofa certain intensity profile when its image spot is displaced along onlythe X or Y axis. If the image spot is displaced in both X and Y, furthermodification will be required, especially if higher measurementprecision is desired. In one example embodiment, an experimentallydetermined relationship in the form of data matrix or matrices betweenthe quadrant detector reported ratiometric result in terms of (X, Y) andthe actual centroid position (X′, Y′) can be established, and a reversedrelationship can be established to convert each (X, Y) data point to anew centroid (X′,Y′) data point.

FIG. 17 shows an example flow diagram that illustrates how calibrationcan be performed to obtain a modified relationship and to result in moreaccurate wavefront aberration measurement. In the first step 1705, awavefront can be created using various means such as from an eye modelor from a wavefront manipulator like a deformable mirror that canproduce different wavefront such as with different divergence andconvergence or with different wavefront aberrations. In the second step1710, the real centroid position (X′, Y′) of different sampledsub-wavefronts can be compared to the experimentally measuredratiometric values (X, Y) to obtain the relationship between (X′, Y′)and (X, Y). Meanwhile, the calibrated wavefront tilt and hence dioptricvalue versus the centroid data point position can be obtained. In thethird step 1715, a measurement can be made of a real eye and theobtained relationship can be used to determine the centroid position andhence the sampled sub-wavefront tilts from the real eye. In the fourthstep 1720, the determined centroid position or tilt of the sampledsub-wavefront can be used to determine the wavefront aberration orrefractive errors of the real eye.

It should be noted that the first and second calibration related stepscan be executed once for each built wavefront sensor system and thethird and fourth steps can be repeated for as many real eye measurementsas one likes. However, this does not mean that the calibration stepsshould be done only once. In fact it is beneficial to periodicallyrepeat the calibration steps.

As one embodiment of the present disclosure, the calibration steps or apartial calibration can be repeated as often as the manufacturer or anend user prefers using an internal calibration target driven by themicroprocessor as shown in FIG. 9A. For example, an internal calibrationtarget can be moved into the optical wavefront relay beam pathtemporarily every time the system is powered up or even before each realeye measurement automatically or manually as desired by the end user.The internal calibration does not need to provide all the data points asa more substantially comprehensive calibration would or can provide.Instead, the internal calibration target only needs to provide some datapoints. With these data points, one can experimentally confirm if theoptical alignment of the wavefront sensor is intact or if anyenvironmental factor such as temperature change and/or mechanical impacthas disturbed the optical alignment of the wavefront sensor.Accordingly, this will determine if a completely new comprehensivecalibration needs to be conducted or if some minor software basedcorrection will be sufficient to ensure an accurate real eye wavefrontmeasurement. Alternatively, the measured reference wavefront aberrationusing an internal calibration target can figure out the inherent opticalsystem aberration that the wavefront sensor optical system has and thereal eye wavefront aberration can be determined by subtracting theoptical system induced wavefront aberration from the measured overallwavefront aberration.

As another embodiment of the present disclosure, a calibration target(internal or external) can also be used to determine the initial timedelay between the SLD firing pulse and the MEMS mirror scanningposition, or the offset angle between the sub-wavefront samplingposition and the MEMS mirror scanning position along a certain wavefrontsampling annular ring. The same calibration steps can also be used todetermine if the SLD firing time is accurate enough with respect to theMEMS scan mirror position, and if there is any discrepancy from acertain desired accuracy, either an electronics hardware basedcorrection or a pure software based correction can then be implementedto fine tune the SLD firing time or the MEMS scanning drive signal.

As still another embodiment of the present disclosure, if thecalibration (internal or external) detects that the optical alignment isoff or if in a real eye measurement case that the eye is found notpositioned at the best position, but within a range that wavefrontmeasurement can still be done with software correction, then softwarebased adjustment can be performed to cater for such a misalignment asexplained with reference to FIG. 4.

In another example embodiment, if 8 sub-wavefronts are sampled around anannular ring of a wavefront produced from either a calibration target orfrom a real eye and it is found that there is a centroid trace centeroffset of the 8 measured sub-wavefront tilts as a result of, forexample, a PSD transverse position shift or a prismatic wavefront tiltof the wavefront from the patient eye (X′(i), Y′(i)), where i=0, 1, 2, .. . , 7, then a translation of the (X′, Y′) Cartesian coordinate can beperformed so that the 8 data points are given a new Cartesian coordinate(Xtr,Ytr) and are expressed as a new set of data points (Xtr(i),Ytr(i)), where i=0, 1, 2, . . . , 7, with the cluster center of thecentroid data points now centered at the new origin (Xtr=0, Ytr=0). Inthis way, any effect that leads to the appearance of an overallprismatic wavefront tilt resulting, for example, from a misalignmentbetween the sub-wavefront sampling aperture and the position sensingdetector/device, can be filtered out from the measured wavefront. As aresult, the rest of the data processing can be focused on figuring outthe refractive errors and/or the higher order aberrations of thewavefront.

Note that sequential wavefront sampling has the inherent advantage thatit can correlate where we are sampling on an annular ring to thedisplacement of each individually sampled sub-wavefront centroidposition.

As described above, the displacements of the centroids of the sampledwavefront portions are determined using the ratiometric X and Y valuescalculated from the output signals generated by the PSD. The positionsof these output values form geometric patterns that can be analyzed bythe front-end or backend electronic processing system to determineophthalmic characteristics of a subject eye. The formation and analysisof these patterns are illustrated in FIG. 9C. In FIG. 9C thedisplacements are depicted as if they were displayed on monitor.However, in other example embodiments the displacements are processed byalgorithms executed as software by the front end processing system andare not necessarily displayed to a user.

FIG. 9C shows a number of representative cases of planar wavefront,defocus and astigmatism, the associated image spot position on thequad-detector behind the sub-wavefront focusing lens, as well as thesequential movement of the corresponding centroid positions whendisplayed as a 2D data point pattern on a monitor. Note that instead ofdrawing a number of shifted wavefronts being sampled and projected asdifferent sub-wavefronts onto the same sub-wavefront focusing lens andthe quad-detector, we have taken the equivalent representation,described above with reference to FIGS. 13A-E, such that a number ofsub-wavefronts are drawn around the same annular ring and accordingly, anumber of quad-detectors are drawn around the same annular ring torepresent the case of scanning different portions of a wavefront to asingle sub-wavefront focusing lens and a single quad-detector.

Assume that we start the scan around the wavefront annular ring from thetop sub-wavefront and move in a clockwise direction to the secondsub-wavefront on the right and so forth as indicated by the arrow 9009.It can be seen from FIG. 9C that when the wavefront is a plane wave9001, all the sub-wavefronts (for example, 9002) will form an image spot9003 at the center of the quad-detector 9004 and as a result, thecentroid trace 9005 on a monitor 9006 will also be always at the originof the x-y coordinate.

When the input wavefront is divergent as shown by 9011, the center ofthe image spot 9013 of each sub-wavefront 9012 will be on the radiallyoutward side from the wavefront center with an equal amount of departurefrom the center of the quad-detector 9014, and as a result, the trace9015 on the monitor 9016 will be a clockwise circle as indicated by thearrow 9018 starting from the top position 9017. If, on the other hand,the input wavefront is convergent as shown by 9021, the center of theimage spot 9023 of each sub-wavefront 9022 will be on the radiallyinward side relative to the center of the wavefront with an equal amountof departure from the center of the quad-detector 9024. As a result, thecentroid trace 9025 on the monitor 9026 will still be a circle but willstart from the bottom position 9027 and will still be clockwise asindicated by the arrow 9028. Hence when a sign change for both thex-axis centroid position and the y-axis centroid position is detected,it is an indication that the input wavefront is changing from adivergent beam to a convergent beam or the other way round. Furthermore,the starting point of the centroid trace can also be used as a criterionto indicate if the input wavefront is divergent or convergent.

It can also be seen from FIG. 9C that when the input wavefront isastigmatic, it can happen that the wavefront can be divergent in thevertical direction as shown by 9031 a and convergent in the horizontaldirection as shown by 9031 b. As a result, the centroid position of thevertical sub-wavefronts 9033 a will be located radially outward withrespect to the center of the input wavefront, and the centroid positionof the horizontal sub-wavefronts 9033 b will be located radially inwardwith respect to the center of the input wavefront. Consequently, thecentroid trace 9035 on the monitor 9036 will start from the top position9037 but move anti-clockwise as indicated by arrow 9038, hence thecentroid trace rotation is now reversed.

Using a similar argument, it is not difficult to figure out that if theinput wavefront is astigmatic but all the sub-wavefronts are eitherentirely divergent or entirely convergent, the rotation of the centroidtrace will be clockwise (i.e. not reversed), however, for the astigmaticcase, the trace of the centroid on the monitor will be elliptic ratherthan circular since the sub-wavefronts along one astigmatic axis will bemore divergent or convergent than those along the other axis.

For a more general astigmatic wavefront, either the centroid trace willrotate in the reversed direction with the trace either elliptical orcircular, or the centroid trace will rotate in the normal clockwiserotation direction but the trace will be elliptical. The axis of theellipse can be in any radial direction relative to the center, whichwill indicate the axis of the astigmatism. In such a case, 4sub-wavefronts around an annular ring may not be enough in preciselydetermining the axis of the astigmatism and more sub-wavefronts (such as8, 16 or 32 instead of 4) can be sampled around an annular ring.

To summarize, for a divergent spherical wavefront versus a convergentspherical wavefront coming, for example, from a human eye, thesequentially sampled sub-wavefronts around an annular ring of the eyepupil will result in the sequential centroid data points being arrangedaround a circle, but with each data point landing at different opposinglocations depending on whether the wavefront is divergent or convergent.In other words, for a divergent wavefront, for example, if we expect acertain data point (e.g. i=0) to be at a certain location (e.g. (Xtr(0),Ytr(0))=(0, 0.5); then for a convergent wavefront of the same ofspherical radius but a different sign, we expect the same data point tobe at an opposing location (e.g. (Xtr(0), Ytr(0))=(0, −0.5). On theother hand, if the original wavefront has both spherical and cylindricalcomponent, the centroid data points will trace out an ellipse that canbe a normal rotation ellipse, a straight line, an abnormal or reverserotation ellipse, and an abnormal or reverse rotation circle. Thesescenarios have been discussed in detail in co-assigned U.S. Pat. No.7,445,335 and co-assigned U.S. Pat. No. 8,100,530.

One embodiment of the present disclosure is to use both positive andnegative values of major and minor axes to describe the centroid datapoints as an equivalent ellipse. For example, an overall divergentwavefront can be defined as having a positive major and minor axis andan overall convergent wavefront can be defined as producing a “negative”major and mirror axis.

FIG. 18 shows a graphical representation of a sequential ellipse usingtrigonometry expressions, where U(t)=a·cos(t), V(t)=b·sin(t), a is theradius of the bigger circle and b is the radius of the smaller circle.As can be seen, with a>b>0 i.e. both a and b are positive, the ellipserotates counter-clockwise. Thus the points on the ellipse can representthe sequentially calculated centroid displacements of an overalldivergent wavefront with both spherical and cylindrical refractive errorcomponents where the degree of divergence is different for thehorizontal and vertical directions. If a=b, the ellipse would representa divergent spherical wavefront where the degree of divergence is thesame for the horizontal and vertical directions. Assume a t₀ value of0<t₀<π/2, the point (U(t₀), V(t₀)) will be in the first quadrant of theU-V Cartesian coordinate.

Note that in this particular example of FIG. 18, as well as in FIGS. 19,20 and 21, we have assumed that the Cartesian coordinate axes U and Vare aligned with the quadrant detector axis x and y, and at the sametime, we have also assumed that the astigmatic axis is along the x or yaxis as well. Therefore the ellipse as shown in FIGS. 18 to 21 isoriented horizontal or vertical.

If the major and minor axes are both negative, we can express them as −aand −b. In this case as shown in FIG. 19, the corresponding sequentialellipse is expressed by U(t)=−a·cos(t), V(t)=−b·sin(t), with a>b>0, both−a and −b negative. This will result in an ellipse that still rotatescounter-clockwise. This can be considered as representing an overallconvergent wavefront with both spherical and cylindrical refractiveerror components where the degree of convergence is different for thehorizontal and vertical directions. If a=b, it would represent aconvergent spherical wavefront where the degree of convergence is thesame for the horizontal and vertical directions. With a t₀ value of0<t₀<π/2, the point (U(t₀), V(t₀)) will now be in the third quadrant ofthe U-V Cartesian coordinate, on the opposite side of the coordinateorigin as compared to that of FIG. 18.

If the major axis is positive and the minor axis is negative, we canexpress them as a and −b. In this case as shown in FIG. 20, thecorresponding sequential ellipse is expressed by U(t)=a·cos(t),V(t)=−b·sin(t), with a>b>0, a positive, and −b negative. This willresult in an ellipse that rotates clockwise starting from the fourthquadrant. This can be considered as representing a horizontallydivergent and vertically convergent wavefront with both spherical andcylindrical refractive error components where the degree of horizontaldivergence and vertical convergence are different. If a=b, it wouldrepresent a horizontally divergent and vertically convergent cylindricalwavefront where the degree of horizontal divergence and verticalconvergence are the same. With a t₀ value of 0<t₀<π/2, the point (U(t₀),V(t₀)) will now be in the fourth quadrant of the U-V Cartesiancoordinate.

If the major axis is negative and the minor axis is positive, we canexpress them as −a and b. In this case as shown in FIG. 21, thecorresponding sequential ellipse is expressed by U(t)=−a·cos(t),V(t)=b·sin(t), with a>b>0, −a negative, and b positive. This will resultin an ellipse that rotates clockwise starting from the second quadrant.This can be considered as representing a horizontally convergent andvertically divergent wavefront with both spherical and cylindricalrefractive error components where the degree of horizontal convergenceand vertical divergence are different. If a=b, it would represent ahorizontally convergent and vertically divergent cylindrical wavefrontwhere the degree of horizontal convergence and vertical divergence arethe same. With a t₀ value of 0<t₀<π/2, the point (U(t₀), V(t₀)) will nowbe in the second quadrant of the U-V Cartesian coordinate, on theopposite side of the coordinate origin as compared to that of FIG. 20.

Note that the assignment of divergent wavefront to “positive” versus“negative” axis is arbitrary and can be reversed, as long as wedistinguish between them. The positive direction of the axes can also beswapped. For example, the U axis can be pointing upward instead ofpointing to the right and the V axis can be pointing to the rightinstead of pointing upward. In this case, as shown in FIG. 22, thesequential centroid data points expected from a divergent sphericalwavefront sampled at the plane represented by the dashed line will be aclockwise circle with the resulting data point position and polarity asindicated by the numbers and the arrows in FIG. 22. Note that thesequential rotation direction is changed as compared to that of FIG. 18due to a different assignment of the axis polarity. Similarly, in thesame case, the sequential centroid data points expected from aconvergent spherical wavefront sampled at the plane represented by thedashed line as shown in FIG. 23 will be a clockwise circle with theresulting data point position and polarity as indicated by the numbersand the arrows in FIG. 23. Note the swapping of the numbered data pointsfrom the original position in FIG. 22 to the opposite position in FIG.23 when the sampled wavefront changes from being divergent to beingconvergent.

One embodiment of the present disclosure is to use a calibration(internal or external) to determine the initial offset angle of the datapoint vector(s) relative to the Xtr or Ytr axes. Another embodiment ofthe present disclosure is to rotate the Cartesian coordinate (Xtr, Ytr)to another Cartesian coordinate (U, V) by the offset angle so that atleast one of the calibration centroid data point, for example, the i=0data point (U(0), V(0)), is aligned on either the U or the V axis of thenew Cartesian coordinate U-V. In this manner, the measured sub-wavefronttilts, now expressed as data points (U(i), V(i)), where i=0, 1, 2, . . ., 7, with at least one of the data points aligned on either the U or Vaxis, can be easily correlated to an ellipse and/or averaged as if theyare on a correlated ellipse, with the ellipse parameters correlated tothe spherical and cylindrical diopter values of the sampled wavefrontand with the major and/or minor axis direction correlated to thecylinder axis of the sampled wavefront.

FIG. 24 shows the Cartesian coordinate translation and rotation from theoriginal X-Y coordinate to the translated Xtr-Ytr coordinate and furtherrotated to the U-V coordinate of 8 sequentially sampled centroid datapoints that are fitted to a sequential ellipse. Note that for an overalldivergent wavefront and the shown coordinate axes selection, thesequential rotation direction is clockwise. In this example, the centerof the 8 sequentially obtained data points is firstly determined and theX-Y coordinate is translated to the Xtr-Ytr coordinate where the originof the Xtr-Ytr coordinate is the center of the 8 sequentially obtaineddata points. Then the major and minor axes of the fitted ellipse (withtheir corresponding axis polarity as discussed before) are obtainedthrough digital data processing and coordinate rotation is performed byaligning the major or minor axis of the fitted ellipse to the U or Vaxis of the U-V coordinate that has the same origin as the Xtr-Ytrcoordinate. Note that in this example, the first data point (point 0) isalready aligned with or located on the U axis. In a more generalsituation, this may not be the case. However, if aligning the first datapoint (point 0) with the U axis helps data processing, the firing timeof the SLD relative to the driving signal of the MEMS scanner can beadjusted to enable this alignment and the phase delay between the twosignals can be used for the simplification of data processing.

The presently disclosed wavefront sampling example around an annularring, the coordinate transformation, and the associated data processinghave the benefit that the sphero-cylinder diopter values can be simplyexpressed analytically as a function of the (U(i), V(i)) data pointvalues and as such, the data processing can be substantially simplifiedand executed extremely fast. In other words, the data points (U(i),V(i)) can now be easily fitted to an ellipse in canonical position(center at origin, major axis along the U axis) with the expressionU(t)=a·cos(t) and V(t)=b·sin(t), where a and b are the major axis andthe minor axis respectively and can have positive or negative values.

This algorithm enables real time high precision measurement of eyewavefront over a large dynamic range. When the U, V axes are rotated tofit the ellipse to the canonical position the orientation of the ellipseindicates the axis of astigmatism. Further, the magnitudes of a and bindicate the relative magnitudes of the divergent and convergentastigmatic components and the direction of rotation helps identifieswhich component is divergent and which component is convergent. As aresult, real time titration of a surgical vision correction procedurecan be performed. In particular, the real time wavefront measurementresults can be used to direct, and/or align, and/or guide the operationof limbal relaxing incision (LRI) and/or astigmatic keratotomy (AK), aswell as toric IOL (intraocular lens) rotation titration.

FIG. 25 shows a special case of FIG. 24, the result of coordinaterotation transformation and 8 centroid data points on the U-Vcoordinate, with the left side corresponding to a divergent sphericalwavefront having equal positive major and minor axes, and with the rightside corresponding to a convergent spherical wavefront, having equalnegative major and minor axes. Note again the swapping of the numbereddata points from the original position to the opposite position when thesampled wavefront changes from being divergent to being convergent.

When there is an astigmatic component superimposed onto a sphericalcomponent, a number of centroid data point trace scenarios occur,depending on the degree of the astigmatic wavefront tilt compared tothat of the spherical wavefront tilt as has been discussed inco-assigned U.S. Pat. No. 7,445,335 and co-assigned U.S. Pat. No.8,100,530. With the above-mentioned Cartesian coordinatetransformations, the centroid data points can trace out a patterncentered at the origin of the U-V coordinate with at least one of thedata points aligned with either the U or the V axis, but with differentelliptic shapes and orientations. The shapes of the pattern include anormal rotation ellipse with both positive major and positive minoraxes, a straight line with a positive or negative major axis or with apositive or negative minor axis, an abnormal or reverse rotation ellipsewith a negative major axis and positive minor axis or with a positivemajor axis and a negative minor axis, and an abnormal or reverserotation circle with either a positive major axis and a negative minoraxis or with a negative major axis and a positive minor axis.

Since we are measuring a sequential wavefront, in the circular tracecase, we can distinguish between three different circular trace patterns(divergent spherical circle, convergent spherical circle, and theastigmatic reverse rotation circle) because axis polarity is determinedby the order in which the wavefront samples are collected. In fact, theastigmatic reverse rotation circle is effectively correlated to anellipse since one axis (major or minor) has a different sign or polaritythan the other axis (minor or major). The orientation of the ellipse orstraight line or the reverse rotation circle can be determined from themajor or minor axis direction and can be at any angle between 0 and 180degree, which is also the practice well accepted by optometrists andophthalmologists. It should be noted that the assignment of the majorand/or minor axis is arbitrary so there is no need for the absolutelength of the major axis to be longer than that of the minor axis. Theassignment is only meant to facilitate the calculation of refractiveerrors associated with a wavefront from an eye.

It should also be noted that in addition to sampling the wavefrontaround one annular ring, multiple annular rings of different diametersor multiple concentric annular rings of the wavefront can be sampled. Indoing so, a 2D wavefront map can be obtained and presented to an enduser. By dynamically changing the annular ring sampling size of thewavefront sensor, one can also confirm the aphakic condition of asubject throughout the entire corneal visual field.

In yet another embodiment, the MEMS scanning mirror can be operated tosample sub-wavefronts in a spiral pattern or concentric rings of varyingradii, allowing the detection of higher-order aberrations. Zernikedecomposition can be performed to extract all the wavefront aberrationcoefficients, including high order aberrations such as trefoil, coma,and spherical aberration. For example, coma can be determined bydetecting a lateral shift of the wavefront as the scan radius isincreased or decreased. If the number of samples per annular ring isevenly divisible by 3, then trefoil can be detected when the dots form atriangular pattern that inverts when the scan radius is increased ordecreased.

The effective spacing between any two wavefront sampling points can becontrolled by controlling the SLD firing time and the drive signalamplitude of the MEMS scan mirror. In addition to reducing the size ofthe sub-wavefront sampling aperture which can be achieved by the frontend processing system if the aperture is electronically variable, higherspatial precision/resolution sampling of the wavefront can also beachieved by precisely controlling the SLD firing time and also reducingthe SLD pulse width as well as increasing the precision in the controlof the MEMS scan mirror amplitude or position. In this respect, the MEMSscan mirror can be operated in closed-loop servo mode with the MEMSmirror scan angle monitor signal being fed-back to the microprocessorand/or the electronics control system to control the scan angle drivesignal to achieve better scan angle control precision. On the otherhand, more averaging can be achieved by increasing the size of thesub-wavefront sampling aperture or even increasing the pulse width ofthe SLD. Therefore, another embodiment of the present disclosure is touse the electronics to control the SLD and the wavefront shifter/scannerto achieve either higher precision/resolution in spatial wavefrontsampling or more averaging in spatial wavefront sampling. Higherprecision/resolution spatial wavefront sampling is desired for highorder aberration measurement and more averaged spatial wavefrontsampling is desired for measuring the refractive errors of the wavefrontin terms of the spherical and cylindrical dioptric values and the axisof cylinder or astigmatism.

It should be noted that the above mentioned Cartesian coordinatetranslation and rotation is only one of many possible coordinate systemtransformations that can be employed to facilitate the calculation ofrefractive errors and wavefront aberrations. For example, non-Cartesiancoordinate such as polar coordinate or non-perpendicular axis basedcoordinate transformations can be used. Therefore, the scope of theconcept of using coordinate transformation to facilitate the calculationof wavefront aberrations and refractive errors should not be limited toCartesian coordinates. The transformation can even be between Cartesiancoordinate and polar coordinate.

In practice, a wavefront from a patient eye can contain higher orderaberrations in addition to sphere and cylinder refractive errors.However, for most vision correction procedures such as cataractrefractive surgery, generally only the sphere and cylinder refractiveerrors are corrected. Therefore, the need for averaging is desired sothat the best sphere and cylinder correction dioptric values andcylinder axis angle can be found and prescribed. The present disclosureis extremely suitable for such an application as by averaging andcorrelating the centroid trace(s) to one or more ellipse(s) over one ormore annular rings, together with the polarity of major and minor axistaken into consideration when correlating the centroid data points tothe ellipse(s), the resultant prescription given in terms of the sphereand the cylinder dioptric values as well as the cylinder axis hasalready included averaging the effect of higher order aberrations. Onthe other hand, the algorithm and data processing can also tell the enduser how much higher order aberration there is in the wavefront bycalculating how close the correlation of the centroid data points to theellipse(s) is.

FIG. 26 shows the process flow diagram of one example embodiment indecoding the sphere and cylinder dioptric values and the cylinder axisangle. The calibration steps, including the step 2605 of moving aninternal calibration target into the wavefront relay path to calibratethe system and getting the offset angle(s), the step 2610 of obtainingthe relationship between SLD pulse delay(s) and the offset anglevalue(s), and the step 2615 of moving the internal calibration targetout from wavefront relay beam path, can be performed once for many realeye measurements such as once per day before any measurement, ormultiple times such as once before each eye measurement, as discussedbefore.

Once the offset angle information is obtained, there is an optional step2620 to change or adjust the offset angle(s), which can be achieved bychanging the SLD pulse delay or the initial phase of the sinusoidal andco-sinusoidal drive signal sent to the MEMS scan mirror. For example,with a spherical reference wavefront, the offset angle can be adjustedsuch that one of the centroid data point is aligned with the X or Y axisand in this case, there is no need to further conduct the coordinaterotation transformation. This can reduce the burden on data processing.

In the next step 2625, the centroid data point positions can be computedas discussed before from A, B, C, D values to ratiometric (X, Y) values,to modified centroid position values (X′, Y′), and to translatedcentroid position values (Xtr, Ytr). The following step 2630, whichinvolves coordinate rotation transformation from (Xtr, Ytr) to (U, V),can be optional if the SLD pulse delay relative to the MEMS mirrorscanning can be controlled so that one of the centroid data point isalready on the Xtr or Ytr axis.

In the next step 2635 in determining if the wavefront is spherical, wecan compare the magnitude or length of some (such a perpendicular pair)or all the centroid data point vectors relative to the (Xtr=0, Ytr=0) or(U=0, V=0) origin in different ways. For example, if the standarddeviation of all vector magnitudes or lengths is below a predeterminedcriteria value (for example, a value that corresponds to less than 0.25Dcylinder), we can treat the wavefront to be spherical. Alternatively, wecan compare the vector magnitudes of some or all the data point vectorsand if their magnitudes are substantially equal and their difference isbelow a predetermined criteria value, then the wavefront can beconsidered as spherical.

In such a spherical wavefront case, as a following step 2640 as shown inFIG. 26, we can still correlate the data points to an ellipse, but inaddition to calculating the major or minor axis length which will besubstantially equivalent, we can average the major and minor axislength, and depending on the sign or polarity of the major and minoraxis which can be both positive or negative, output an averaged positiveor negative spherical diopter value. Note that the relationship betweenthe dioptric value and the major or minor axis length can be and shouldhave been obtained during the comprehensive calibration stage as hasbeen discussed before.

An optional follow-up step 2645 is to display the computed sphericaldioptric value quantitatively as a number and/or qualitatively ascircle, with the circle diameter or radius representing the absolutespherical dioptric value, and with the sign of the sphere being shownusing for example a different color or line pattern for the circle.

On the other hand, if the wavefront is found not spherical, we canassume that there is an astigmatic component. As a follow-up step 2650,we can correlate the data points to an ellipse and calculate the majorand minor axis length with polarity as the value can be positive ornegative, as well as an ellipse angle which can be either the major orminor axis angle. Having calculated the ellipse angle, the major andminor axis lengths, we can compute sphere and cylinder dioptric valuesusing the experimentally obtained calibration relationship or a look-uptable. It is preferred that the diopter values are monotonically relatedto the major and minor axis length (with polarity or sign informationincluded) so that there are only unique solutions for a certain ellipse.As in the case of spherical wavefront, an optional follow-up step 2655is to display the computed spherical and cylindrical dioptric values andthe cylinder axis quantitatively as a set of numbers and/orqualitatively as a circle plus a straight line, with the circle diameterrepresenting the sphere dioptric value, with the straight line lengthrepresenting the cylinder dioptric value, and with the straight lineorientation angle which can be indicated by a long thin or dashed lineor an arrow, representing the cylinder axis angle. Alternatively, thequalitative display can also be in the form of an ellipse with eitherthe major or the minor axis length representing the sphere dioptricvalue, with the difference in major and minor axis length (polarityconsidered) representing the cylinder dioptric value, and with theellipse orientation angle representing the cylinder axis angle. Again,the sign of the sphere and cylinder dioptric value can be shown using,for example, a different color or a different line pattern for thecircle-plus-straight-line representation or for the ellipserepresentation. One embodiment of the present disclosure is to allowuser selection of an ellipse or a circle-plus-straight-line to representthe refractive errors of a patient eye.

It should be noted that there can be many other ways to qualitativelydisplay the refractive errors. The above mentioned qualitativerepresentations are only illustrative rather than comprehensive. Forexample, the representation can also be an ellipse with its major axisproportional to one independent cylinder diopter value and its minoraxis proportional to another independent and perpendicular cylinderdiopter value. In addition, the axis angle representing one cylinder orthe other cylinder angle can be the original angle or shifted by 90°, asthe cylinder axis angle can be either the major axis angle or the minoraxis angle depending on whether the end user prefers a positive ornegative cylinder prescription. Alternatively, the representation canalso be two orthogonal straight lines with one straight line lengthproportional to one independent cylinder dioptric value and the otherorthogonal straight line length proportional to the other independentand perpendicular cylinder dioptric value.

As mentioned before, one embodiment of the present disclosure is theoverlay, on the live video image of the patient's eye, of the wavefrontmeasurement result in a qualitative and/or quantitative way. Thedisplayed ellipse or straight-line angle can also be dependent on theorientation of the surgeon/clinician relative to the patient's eye(superior or temporal), and if temporal, which of the patient's eyes isbeing imaged (right or left). For cataract surgery, it is preferred thatthe cylinder axis presented to a cataract surgeon is aligned with thesteeper axis of the cornea so that the surgeon can conduct LRI (LimbalRelaxing Incision) based on the presented axis direction.

The live eye image can be processed with a pattern recognition algorithmto achieve eye registration for supine or vertical patient positionand/or to determine the axis of an implanted tonic IOL referenced toiris landmarks such as crypt. In addition, the live image can also beused to identity particular lens (natural or artificial) registrationsfor alignment and/or comparison of optical signals (from, for example,wavefront and/or OLCI/OCT measurement) to physical features of the eyelens or iris.

Also note that the conversion from the correlated ellipse major andminor axis length to the diopter values can be done in different waysdepending on the preference of the end user. As is well known to thoseskilled in the art, there are three ways to represent the samerefractive error prescription. The first is to represent it as twoindependent perpendicular cylinders, the second one is to represent itas sphere and a positive cylinder, and the third one is to represent itas a sphere and a negative cylinder. In addition, the representation canbe with respect to either prescription or the actual wavefront. Ourcorrelated ellipse actually directly provides the dioptric values of thetwo independent perpendicular cylinders. As for the conversion from oneway of representation to another, it is well known to those skilled inthe art. What needs to be emphasized is that one embodiment of thepresent disclosure is the use of both positive and negative values torepresent the major and minor axis of the correlated ellipse and thecalibration approach to correlate the major and minor axis length, whichcan be either positive or negative, to the two independent perpendicularcylinder dioptric values which can also be positive or negative.

Note that optometrists, ophthalmologists, and optical engineers mayrepresent the same wavefront at the cornea or pupil plane of a patienteye using different ways. For example, an optometrist generally prefersa prescription representation which is the lens(se) to be used to cancelout the wavefront bending to make it planer or flat; an ophthalmologisttends to prefer a direct representation which is what the wavefront atthe eye cornea plane is in terms of sphere and cylinder dioptric valuesand cylinder axis; while an optical engineer would generally not usedioptric values but a wavefront map that shows the 2D deviation of thereal wavefront from a perfect planar or flat wavefront, or arepresentation using Zernike polynomial coefficients. One embodiment ofthe present disclosure is the mutual conversion between these differentrepresentations that can be carried out by the end user as the algorithmhas been built in the device to do such conversion, so it is up to theend user to select the format of the representation.

In terms of further improving the signal to noise ratio and hencemeasurement accuracy and/or precision, the ellipse orcircle-plus-straight-line correlation can be done for one frame (or set)of data points or multiple frames (or sets) of data points.Alternatively, the obtained sphere and cylinder dioptric values as wellas the cylinder axis angle can be averaged over multiple captures. Forexample, the averaging can be accomplished simply by adding respectivelya given number of sphere and cylinder dioptric values of multiplemeasurements and dividing by the given number. Similarly, the cylinderangle can also be averaged although it can be more involved because ofthe wrap-around problem near 0°, as we report angles from 0° to 180°. Asone approach, we use trigonometric functions to resolve this wrap-aroundissue.

It should be noted that the front-end processing system as indicated inFIG. 7 also controls the international fixation target in addition toother LEDs. However, the internal fixation does not need to be limitedto a single LED or a single image such as a back-illuminated hot airballoon. Instead, the internal fixation target can be a micro-displaycombined with an eye accommodation enabling optical element such as afocus variable lens. The patient eye can be made to fixate at differentdirections by lighting up different pixels of the micro-display so thatperipheral vision wavefront information such as a 2D array of wavefrontmaps can be obtained. In addition, the patient eye can be made to fixateat different distances to enable the measurement of the accommodationrange or amplitude. Furthermore, the fixation micro-display target canbe controlled to flash or blink with various rates or duty cycles, andthe micro-display can be a colored one to enable fixation target tochange color and to light-up pattern or spots.

As mentioned before, one embodiment of the present disclosure is intracking the eye. FIG. 27 shows an example process flow diagram of aneye tracking algorithm. The steps involved include step 2705 ofestimating the position of the eye pupil using either the eye pupilposition information from the live eye pupil or iris image or othermeans such as detecting specular reflection from the cornea apex byscanning the SLD beam in two dimensions; step 2710 of adjusting the SLDbeam scanner to follow the eye movement; step 2715 of offsetting the DCdrive component of the wavefront scanner/shifter in proportion to theSLD beam adjustment to compensate the eye pupil movement so that thesame intended portions of the wavefront from the eye are always sampledregardless of the eye movement; and as an option, step 2720 ofcorrecting the measurement of wavefront aberration. The live imagecamera provides a visual estimate of either (a) the center of the iris,or (b) the center of the corneal limbus. By correlating the SLD beam (X,Y) positions to the visual field of view, the SLD can be directed to thesame position on the cornea. Typically for wavefront sensing, thisposition is slightly off the axis or apex of the cornea as in this way,specular reflection of the SLD beam will generally not be directlyreturned to the position sensing detector/device of the wavefrontsensor. The center of the iris or the center of the limbus can be usedas a reference point to directing the SLD beam.

Note that a unique feature of the presently disclosed algorithm is thestep of offsetting the DC drive component of the wavefrontscanner/shifter in proportion to the SLD beam adjustment. This is acritical step as it can ensure that the same portions of the wavefront(such as the same annular ring of the wavefront) from the eye aresampled. Without this step, as the eye is transversely moved, differentportions of the wavefront from the eye will be sampled and this cancause significant wavefront measurement errors. The reason why the laststep of correcting the measurement of wavefront aberration is optionalis that with the compensation that can be provided by the wavefrontscanner/shifter in proportion to the SLD beam adjustment, theconsequence to the wavefront measurement is that there will be addedastigmatism and/or prismatic tilt and/or other know aberrationcomponents to all the sampled portions of the wavefront which can bepre-determined and taken into consideration. We have shown that ourrefractive error decoding algorithm can automatically average theaberration to figure out compromised sphere and cylinder and to filterout the prismatic tilt through coordinate translation, so for refractiveerror measurements, there is no additional need for prismatic tiltcorrection. In spite of the fact that the amount of coordinatetranslation is already an indication of the prismatic tilt of thewavefront from the eye, for a complete wavefront measurement whichshould include the prismatic tilt, this additional astigmatism and/orprismatic tilt and/or other know aberration components caused by eyetracking should be subtracted out, so the last correction step mightstill be needed.

Another embodiment of the present disclosure is in adaptively selectingthe diameter of the wavefront sampling annular ring so that whilewavefront sampling is only performed within the eye pupil area, theslope sensitivity of the response curve as a function of the annularring diameter can also be exploited to provide higher measurementsensitivity and/or resolution. In general, among all the dioptric valuesof different wavefront aberrations such as sphere, cylinder and trefoil,the sphere dioptric value generally requires the largest coverage rangeas it can vary a lot among different eyes as well as during a cataractsurgery when the natural eye lens is removed (i.e. the eye is aphakic).On the other hand, when a cataract surgery is completed or nearcompletion with an IOL (intraocular lens) implanted in the eye, thewavefront from the eye should be close to planar as the pseudo-phakiceye should in general be close to emmetropia. For a typicalauto-refraction measurement, the wavefront from only the 3 mm diametercentral area of the eye pupil is generally sampled. A wavefront sensorcan therefore be designed to provide enough diopter measurementresolution (e.g. 0.1D) as well as enough diopter coverage range (e.g.−30D to +30D), over an effective wavefront sampling annular ring areathat covers for example, a diameter range from 1 mm to 3 mm. Meanwhile,in order confirm emmetropia with higher sensitivity and/or wavefrontmeasurement resolution, we can expand the wavefront sample annular ringto a diameter of, for example, 5 mm near the end of a cataractrefractive surgery as long as the pupil size is large enough to moreaccurately measure the wavefront or refractive errors of a pseudo-phakiceye.

FIG. 28 shows an embodiment flow diagram of an algorithm that canimplement this concept. The steps involved include the step 2805 ofusing the eye pupil information obtained from the live eye image toestimate the eye pupil size, the step 2810 of using the eye pupil sizeinformation to determine the maximum diameter of the wavefront samplingannular ring, and the step 2815 of increasing the annular ring diameterup to the maximum diameter as determined by step 2810 for pseudo-phakicmeasurement to achieve better diopter resolution. This “zoom in” featurecould be user-selectable or automatic. In addition, we can also use thePSD ratiometric output to adaptively adjust the annular ring diameterfor optimal dioptric resolution and dynamic range coverage.

One feature of the present disclosure is to combine the live eye image,with or without a pattern recognition algorithm, with the wavefrontmeasurement data, to detect the presence of eye lids/lashes, iris,facial skin, surgical tool(s), surgeon's hand, irrigation water or themoving away of the eye from the designed range. In doing so, “dark” or“bright” data can be excluded and the SLD can be smartly turned on andoff to save exposure time, which can enable higher SLD power to bedelivered to the eye to increase the optical or photonic signal to noiseratio. FIG. 29 shows an example process flow diagram illustrating such aconcept. The steps involved include the step 2905 of using either thelive eye image and/or the wavefront sensor signal to detect the presenceof unintended object in the wavefront relay beam path or the moving awayof the eye from a desired position and/or range, the step 2910 ofabandoning the erroneous “bright” or “dark” wavefront data, the step2915 of turning the SLD off when the wavefront data is erroneous, and anoptional step 2920 of informing the end user that the wavefront data iserroneous or invalid.

Another embodiment of the present disclosure is in scanning and/orcontrolling the incident SLD beam across a small area on the retina toremove speckles, do averaging, and also potentially allow an increase inthe optical power within the safety limit that can be delivered into theeye, which can increase the optical signal to noise ratio. In addition,the SLD beam divergence/convergence and hence the size of the SLD beamspot size on the retina can also be dynamically adjusted using, forexample, an axially movable lens or a focus variable lens or adeformable mirror so that the SLD spot size on the retina can becontrolled to enable a more consistent and/or well calibratedmeasurement of the wavefront from the eye. Meanwhile, the SLD beam spotsize and/or shape on the retina can also be monitored using, forexample, the same live eye image sensor by adjusting its focus or adifferent image sensor solely dedicated to monitoring the SLD beam spoton the retina of an eye. With such a feedback and the incorporation of aclosed loop servo electronics system, the static or scanned pattern ofthe SLD spot on the retina can be controlled.

Still another embodiment of the present disclosure is to include a laseras a surgery light source that can be combined with the SLD beam to belaunched through the same optical fiber or another free space light beamcombiner that can use the same the SLD beam scanner or a differentscanner to scan the surgery laser beam for performing refractivecorrection of the eye such as LRI (limbal relaxing incision). The samelaser or a different laser can also be used to “mark” the eye or “guide”the surgeon, i.e. “overlaying” on the eye so that the surgeon can seethe laser mark(s) through the surgical microscope.

Another embodiment of the present disclosure is in measuring the eyedistance while the eye wavefront is being measured and in correcting themeasurement of the wavefront from the eye when the eye distance ischanged. The information on eye distance from the wavefront sensormodule is especially important for a cataract refractive surgery becausewhen the natural lens of the eye is removed, i.e. the eye is aphakic,the wavefront from the eye is highly divergent, and as a result, a smallaxial movement of the eye relative to the wavefront sensor module caninduce a relatively large change in the refractive error or wavefrontaberration measurement. We have discussed how a correction to thewavefront can be done if the eye is transversely moved away from thedesigned position. A similar correction should also be made when the eyeis axially moved away from its designed position. In doing the axialcorrection, either a low optical coherence interferometer (LOCI) or anoptical coherence tomographer (OCT) can be included in the wavefrontsensor module and be used to measure the eye axial distance.Alternatively, a simpler technique of using optical triangulation tomeasure the eye distance can also be employed. LOCI and OCT arepreferred because in addition to eye distance, they can also do eyebiometric/anatomic measurements. These measurements are especiallyvaluable to eye refractive surgery as they can also reveal the effectivelens (natural or artificial) position, if there is tilt in the lens, theanterior chamber depth, the thickness of the cornea and the lens andalso the eye length. With transverse scanning as can be achieved by anOCT system, even the corneal and/or eye lens (natural or artificial)refractive power can be derived in tandem or independently, especiallyfor the case of an aphakic eye.

Still another embodiment is to combine two or more of the measurementresults obtained by the wavefront sensor, the eye imaging camera and theLOCl/OCT for other purposes. In one embodiment, the combined informationcan be used to detect optical scattering and/or opacity within the mediaof the ocular system, such as cataract opacity and the presence ofoptical bubbles in the eye, especially after the natural eye lens hasbeen fractured by a femto-second laser. The combined information canalso be used to detect the aphakic state of the eye and to calculate theIOL prescription needed for target refraction in real time in theoperating room (OR) either on demand or right before the IOL isimplanted, and/or to confirm the refraction, and/or to find out theeffective lens position right after the IOL is implanted. Furthermore,the combined information can also be used to determine the alignment ofthe patient head, i.e. to determine if the eye of the patient is normalto the optical axis of the wavefront sensor module. In addition, thecombined information can also be used to perform dry eye detection andto inform the surgeon when to irrigate the eye. Moreover, the combinedinformation can also be displayed per the customization by theclinician/surgeon in order to present to him/her only the preferredinformation, such as eye refractive errors before surgery, IOLprescription at the aphakic state, and end point indicator to indicatefor example, if a targeted eye refraction is reached at the end of asurgery, or if a multi-focal IOL is properly centered withoutsignificant tilt, or when a tonic IOL is implanted, if it is centeredand rotated to the correct axis angle. The display can also show a dataintegrity indicator or a confidence indicator.

The combined information can further be used to determine if the eye isaligned well, and if not, to include a directional guide in the displayto tell a surgeon/clinician which way to move the patient eye or themicroscope for better alignment. The information can also be used toindicate if the eye lid is closed, or if there is/are optical bubble(s)or remains of fractured/ruptured eye lens material inside the eye bagthat may affect the wavefront measurement result, and to includeconfidence indicators in the display to indicate if the wavefrontmeasurement is qualified.

Referring back to FIG. 2, it can be noted that the sub-wavefrontfocusing lens 220 can also be controlled by the electronics system. Thislens can be a focus variable lens or an axially movable lens or even adeformable mirror. The purpose of making this lens active is todynamically adjust its focal length in either an open loop or a closedcontrol loop manner so that the image/light spot size formed by thesub-wavefront focusing lens can be controlled based on the localdivergence or convergence of the sequentially sampled sub-wavefront.This is especially true when wavefront sampling is performed around anannular ring. For example, to achieve better response slope sensitivityfor better wavefront tilt measurement in precision and/or accuracy, theimage spot can be better focused on a the PSD (quadrant detector orlateral effect position sensing detector) that is used to determine thetransverse movement of the image spot. Alternatively, the image spot ofthe sampled sub-wavefront landing on the PSD (quadrant detector orlateral effect position sensing detector) can also be controlled to acertain desired size. For example, one choice for the spot size is thatof a single quadrant of a quadrant detector as is well known to thoseskilled in the art. Another possible choice is a size that produces acompromised high sensitivity and large dynamic response range. Stillanother choice is an image spot size about twice the gap size of thequadrant detector. These different image spot sizes can be dynamicallyvaried depending on the averaged local divergence or convergence of thesequentially sampled sub-wavefront.

By dynamically compensating the wavefront or DC offsetting the defocusof the wavefront, the image spot can also be made to always land at ornear the center of the quadrant detector. With this approach, one shouldbe able to lock and null the image spot of each sampled sub-wavefront insize and position so that the highest sensitivity can be achieved. Thedrive signal for the wavefront compensating or defocus offsettingdevice, the wavefront shifter and the sub-wavefront focusing lens can beused to precisely determine the wavefront tilt of each sampledsub-wavefront.

It should be noted that the presently disclosed apparatus can accomplisha large number of additional tasks depending on the configuration of thehost computer that processes the wavefront data, the eye image data, theeye distance data, the low coherence interferometer data, etc. Forexample, the host computer can be configured to analyze the wavefrontdata to obtain metrics such as refractive errors, to display the metricsqualitatively and/or quantitatively on the display, and to allow thesurgeon/clinician to select the manner in which the qualitative and/orquantitative metrics is to be displayed. In terms of how the wavefrontmeasurement should be displayed, the end user can opt for display ofwavefront aberration versus refraction versus prescription, and/orpositive cylinder versus negative cylinder, and/or end pointindicator(s) such as emmetropia.

The host computer can also be configured to allow the surgeon/clinicianto flip or rotate the live patient eye image/movie to a preferredorientation. In addition, the surgeon/clinician can also rewind andreplay desired recorded segments of a composite movie that may includethe eye image, the wavefront measurement result and even the lowcoherence interferometry measurement results, on demand during or afterthe surgery.

Most importantly, the present disclosure can guide a surgeon to titratethe vision correction procedure in real time to optimize the visioncorrection procedure outcome. For example, it can guide a surgeon inadjusting the IOL position in the eye in terms of centration, tilt andcircumferential angular orientation positioning until the measurementconfirms optimal placement of the IOL. Moreover, it can guide a surgeonin rotating an implanted tonic intraocular lens (IOL) tocorrect/neutralize astigmatism. It can also guide a surgeon inconducting limbal/corneal relaxing incision or intrastromal lenticulelaser (Flexi) to titrate and thus neutralize astigmatism.

The presently disclosed apparatus can also be used to indicate whetheran implanted multi-focal IOL has the desired focusing range in additionto optimizing its positioning. It can also be used to measure whether animplanted AIOL (accommodating or accommodative IOL) can provide adesired accommodation range.

On the display, a real time guide can be provided on how a visioncorrection procedure should proceed in order to facilitate removal ofremaining aberration(s), confirm the results, and document the value andsense of the aberrations. The real time information displayed can alsobe digitally “zoomed out” or “zoomed in” automatically or manually toalert a surgeon or vision correction practitioner that the correctionprocedure is going in the wrong or right direction. When a certain levelof correction has been reached, the displayed information can turn intoa highlighted form in terms of, for example, font size, boldness, styleor color, to confirm intra-operatively that a refractive endpoint goalfor a patient such as emmetropia has been reached.

In addition to visual feedback, audio feedback can also be used solelyor in combination with video feedback. For example, audio informationcan be provided with or without video/graphic information to indicatewhich direction to move an IOL for proper alignment or which directionto rotate a tonic lens to correct/neutralize astigmatism. Also areal-time audio signal can be generated to indicate the type ofrefractive error, magnitude of error, and change in error. The pitch,tone and loudness of the real-time audio signal can be varied toindicate improvement or worsening of applied corrections during thevision correction procedure. A specific pitch of the real-time audiosignal can be created to identify the error as, for example, cylinderwith a tone that indicates the magnitude of the cylinder error.

One very important application of the present disclosure is in helping acataract surgeon in determining, at the aphakic state of a patient'seye, if the pre-surgery selected IOL power is correct or not. The realtime aphakic wavefront measurement (preferably together with the eyebiometry measurement such as that provided by a built-in low coherenceinterferometer) can more accurately determine the IOL power needed andthus confirm whether the IOL power selected pre-surgically is correct ornot, especially for patients with post-op corneal refractive proceduresfor whom the pre-surgery IOL selection formulas do not deliverconsistent results.

Another important application of the present disclosure is in monitoringand recording of the changes in the cornea shape and other eyebiometric/anatomic parameters during the whole session of a cataractsurgery while the wavefront from the patient eye is measured. Thechanges can be measured before, during, and after a cataract surgery inthe OR (operating room) and can be in corneal topography and thicknessas can be measured with keratometry and pachymetry, anterior chamberdepth, lens position and thickness, as a result of various factors thatcan cause a change in the wavefront from the patient eye. These factorsinclude, for example, topical anesthesia, eye lid speculum,incision/wound made in the cornea, anterior chamber filling material,intra-ocular pressure, water/solution irrigation onto the cornea, woundsealing, even wound healing effect and surgeon induced wavefront changeeffect resulting from surgeon specific cataract surgery practice.

The data on the change in the eye biometric/anatomic parameters can beused to compensate for the effects induced by the various factors. Thewavefront outcome after the healing of the incision/wound can thus bepredicted and be used to set certain desired target eye refraction forthe cataract surgery. The right-before-surgery and right-after-surgerycornea shape and other eye biometric/anatomic parameters can be measuredusing the built-in OCT and eye camera and a built-in or external cornealtopographer/keratometer that can be attached either to a surgicalmicroscope or the presently disclosed apparatus. Theright-before-surgery measurement can be done in the OR when the patientis in the supine position before and after topical anesthesia isapplied, before and after an eye lid speculum is engaged to keep the eyelids open. The during-surgery measurements can be done in the OR afterincision(s) is(are) made in the cornea, after the cataract lens isremoved and the anterior chamber is filled with a certain gel (OVD,Ophthalmic Viscosurgical Device) before an artificial intraocular lensis implanted, after an IOL is implanted but before the incision wound issealed. The right-after-surgery measurement can be done in the OR aswell when the patient is still in the supine position right after thesurgeon has sealed the incision/wound but before the eye lid speculum isremoved, and after the eye lid speculum is removed.

The data thus obtained on the changes in the cornea shape and other eyebiometric/anatomic parameters can be combined with the ocular wavefrontmeasurement data and be saved in a data base. Another round ofmeasurements can be done after the incision(s)/wound has/have completelyhealed weeks or months after the surgery and the difference or change inthe ocular wavefront and the cornea shape and/or the eye biometryparameters can also be collected. A nominal data base can therefore beestablished and processed to figure out the target refraction rightafter a cataract surgery that needs to be set in order to result in afinal desired vision correction outcome after the wound has completelyhealed. In this way, all the effects, including even surgeon-inducedaberrations such as astigmatism resulting, for example, from aparticular personalized cornea incision habit, would have been takeninto consideration.

The presently disclosed wavefront sensor can be combined with a varietyof other ophthalmic instruments for a wide range of applications. Forexample, it can be integrated with a femto-second laser or an excimerlaser for LASIK, or eye lens fracturing, or for alignment and/orguidance on “incision”, or for close loop ablation of eye tissues. Thelive eye image, OLCI/OCT data, and the wavefront data can be combined toindicate if optical bubble(s) is/are present in the eye lens or anteriorchamber before, during and after an eye surgical operation.Alternatively, the wavefront sensor can also be integrated with oradapted to a slit lamp bio-microscope.

The present invention can also be integrated or combined with anadaptive optics system. A deformable mirror or LC (liquid crystal) basedtransmissive wavefront compensator can be used to do real time wavefrontmanipulation to compensate some or all of the wavefront errors partiallyor fully.

In addition, the presently disclosed wavefront sensor can also becombined with any other type of intra-ocular pressure (IOP) measurementmeans. In one embodiment, it can even be directly used to detect IOP bymeasuring the eye wavefront change as a function of a patient's heartbeat. It can also be directly used for calibrating the IOP.

These embodiments could also be deployed to measure optics, spectaclesand/or glasses, IOL and/or guide the cutting/machining devices thatcreate the optics. These embodiments could also be adapted tomicroscopes for cell and/or molecular analysis or other metrologyapplications. The present invention can also be used for lens crafting,spectacle confirmation, micro-biology applications etc.

Although various embodiments that incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

What is claimed is:
 1. A wavefront sensor comprising: a light sourceconfigured to output a light beam to illuminate a subject eye; a lightsource driver circuit coupled to the light source, configured to outputa light source drive signal at a first pulsing frequency; a positionsensitive detector having a plurality of detector elements configured tooutput a plurality of detector output signals indicating signal strengthof incident light on each detector element; a beam deflecting elementconfigured to intercept a wavefront beam returned from a subject eyewhen the subject eye is illuminated by the light source and configuredto direct a portion of the wavefront beam from the subject eye throughan aperture toward the detector, where the portion of the wavefront beamdirected through the aperture forms a spot on the detector, where anamplitude of deflection of a centroid of the spot from a reference pointon the detector is approximately indicated by a ratiometric combinationof the signal strengths, and where the amplitude of the deflectionindicates the degree of tilt or convergence or divergence of the portionof the wavefront from a plane wave; a beam deflecting element drivingcircuit, coupled to the beam deflecting element, configured to output abeam deflecting element drive signal to scan the portion of thewavefront beam at a wavefront scanning frequency; and a plurality ofcomposite transimpedance amplifiers, each having an input coupled toreceive one of the plurality of detector output signals and an outputfor providing an amplified detector output signal, with the output ofeach transimpedance amplifier phase-locked to the light source drivesignal and the beam deflecting element drive signal.
 2. The wavefrontsensor of claim 1 with each composite transimpedance amplifiercomprising a low pass filter to increase stability and reduce highfrequency noise.
 3. The wavefront sensor of claim 2 with the low passfilter comprising: a first operational amplifier U2A having an input andoutput; a first resistor R3; and a first capacitor C3 with the firstresistor and capacitor connected in series between the input and outputof the first operational amplifier.
 4. The wavefront sensor of claim 3with the composite transimpedance amplifier further comprising: a secondoperational amplifier U1A having an input and an output; and a feedbackresistor R1, having a feedback resistance value, coupling the output ofthe first operational amplifier to the input of the second operationalamplifier where the amplitude of the amplified detector output signal isproportional to R1 and the noise is proportional to the square root ofR1.